1. Amoako Nkansah Isaac NMTC Berekum
NERVOUS SYSTEM
Amoako Nkansah Isaac
NMTC
Berekum

2. INTRODUCTION
Feeling, thinking, remembering, moving and being aware of the world require activity from the nervous system.
This vast collection of cells also helps coordinate all other body functions to maintain homeostasis and to enable the body respond to changing conditions.
Sensory receptors bring information from within and outside the body to the brain and spinal cord which then stimulates responses from muscles and glands.

3. NEURONES
The nervous system consists of masses of nerve cells called neurones. These cells are the structural and functional units of the nervous system. Neurones typically have a rounded area called the cell body and two types of extensions: dendrites and axons. Neurones vary considerably in shape and size but all have common features.
Dendrites which may be numerous, receive electrochemical messages to the neurone cell body.
Axons are extensions that send information in the form of nerve impulses. Usually a neurone has only one axon. Nerves are bundles of axons.

5. CELL BODIES
The neurone cell body consists of granular cytoplasm, a cell membrane and organelles such as mitochondria, lysosomes, nucleus, etc. cell bodies form the gray mater of the nervous system and are found at the periphery of the brain and in the centre of the spinal cord.
Groups of cell bodies are called nuclei in the CNS and ganglia in the PNS.

6. AXON AND DENDRITES
Dendrites are usually short and highly branched. These processes together with the membrane of the cell body are the neurones main receptive surfaces with which axons from other neurones communicate.
The axon usually arises from a slight elevation of the cell body called the axonal hillock. The axon conducts nerve impulses away from the cell body. Membrane of the axon is called axolemma.
An axon originates as a single structure but may give off side branches (collaterals). Its end may branch into many fine extensions that contact the receptive surfaces of other cells.

7. Larger axons of peripheral neurones are enclosed in sheaths composed of many Schwann cells. These cells wind tightly around axons coating them with many layers of cell membrane that have little or no cytoplasm between them.
The portions of the Schwann cells that contain most of the cytoplasm and the nuclei remain outside the myelin sheath and comprise a neurilemma or neurilemma sheath which surrounds the myelin sheath. Narrow gaps between Schwann cells are called nodes of ranvier.

8. Axons with myelin sheath are called myelinated and those without myelin are unmyelinated.
Myelin is also found in the CNS where groups of myelinated axons appear white and masses of such axons form the white matter. Unmyelinated axons and cell bodies form gray matter within the CNS.

9. CLASSIFICATION OF NEURONES
Neurones differ in structure, size and shape of their cell bodies. They also vary in the length and size of their axons and dendrites and in the number of connections they make with other neurones.
On the basis of structural differences, neurones are classified into 3 major groups.

10. Multipolar neurones have many processes arising from their cell bodies
Multipolar neurones have many processes arising from their cell bodies. Only one process of each neurone is an axon the rest are dendrites.
Most neurones whose cell bodies lie within the brain or spinal cord are multipolar.

11. Bipolar neurones have only two processes, one arising from each end of the cell body. These processes are structurally similar, but one is an axon and the other a dendrite. Neurones within specialized parts of the eyes, nose and ears are bipolar

12. Unipolar neurones have a single process extending from the cell body
Unipolar neurones have a single process extending from the cell body. A short distance from the cell body, this process divides into two branches which really function as a single axon. One branch is associated with dendrites near a peripheral body part. The other branch enters the brain or spinal cord.

14. On the basis of functional differences, neurones are grouped as follows:
Sensory (afferent neurones): they carry nerve impulses from peripheral body parts into the brain or spinal cord. Sensory neurones either have specialized receptor ends at the tips of their dendrites or they have dendrites that are closely associated with receptor cells in the skin or in sensory organs. Most sensory neurones are unipolar; some are bipolar.

15. Interneurones (also called association neurones) lie entirely in the brain or spinal cord. They are Multipolar and link other neurones. Interneurones transmit impulses from one part of the brain or spinal cord to another. That is, they may direct incoming sensory impulses to appropriate parts for processing and interpretation. Other incoming impulses are transferred to motor neurones.

16. Motor (efferent neurone) are Multipolar and carry nerve impulses out of the brain or spinal cord to effectors. Motor impulses stimulate muscles to contract and glands to release their secretions.

17. NEUROGLIAL CELLS
Neurones cannot exist without neuroglial cells which fill spaces, provide structural support or framework, produce fatty lipoprotein myelin and carry on phagocytosis. They also provide nutrients for the neurones. In the CNS, neuroglial cells greatly outnumber neurones and are of the following types

18. Microglial cells are scattered throughout the CNS
Microglial cells are scattered throughout the CNS. They support neurones and phagocytize bacterial cells and cellular debris.
Oligodendrocytes align along nerve fibers. They provide insulating layers of myelin called myelin sheath around axons within the brain and spinal cord.

19. Astrocytes, commonly found between neurones and blood vessels provide structural support, join parts by their abundant cellular processes and help regulate the concentrations of nutrients and ions within the tissue. Astrocytes also form scar tissues that fill spaces following injury to the CNS.
Ependymal cells form an epithelia- like membrane that covers specialized brain parts (choroid plexuses) and forms the inner linings that enclose spaces within the brain (ventricles) and spinal cord(central canal).

20. NERVES
Nerves are bundles of axons. An axon is often referred to as nerve fiber. A nerve therefore is a cordlike bundle of nerve fibers within layers of connective tissue.
Nerves that conduct impulses to the brain or spinal cord are called sensory nerves and those that carry impulses to muscles or glands are called motor nerves. Most nerves include both sensory and motor fibers and are called mixed nerves.

21. CELL MEMBRANE POTENTIAL
The surface of a cell membrane (including a non stimulated or resting neurone) is usually electrically charged or polarized, with respect to the inside.
This polarization arises from an unequal distribution of positive and negative ions between sides of the membrane, and it is particularly important in the conduction of nerve impulses and conduction of muscle impulses.
When the axon is not conducting an impulse, a potential difference across the membrane equals to about -65mV.

22. This reading indicates that the inside of the membrane is negative compared to the outside. This is called the resting membrane potential.
The unequal distribution of these ions is due to the action of the Na+/K+ pump, a membrane protein that actively transports Na+ out of and K+ into the axon. Since the membrane is more permeable to K+ than to Na+, there are always more positive ions outside the membrane than inside.
The cytoplasm of the cell has many large negatively charged particles, including phosphate, sulphate ions and proteins that cannot diffuse across the membranes also contributing to the potential difference.

23. ACTION POTENTIAL
An action potential is a rapid sequence of depolarization and repolarization across an axon membrane as nerve impulses occur.
An action potential is an all or none phenomenon. If a stimulus causes the membrane to depolarize to a certain level, called a threshold, an action potential occurs.
The strength of an action potential does not change, but an intense stimulus can cause an axon to fire more often in a given time interval than a weak stimulus. Action potential requires two types of gated channel proteins in the membrane to open.

24. Na+ channel: when an action potential occurs, the gate of Na+ channels open first and Na+ flows into the axon. As Na+ moves to inside the axon the membrane potential change from -65mV to +40mV. This is termed as depolarization because the charge changes from negative to positive.
K+ channel: potassium channels then opens and K+ flows to outside the axon. This changes the action potential from +40mV back to -65mV. This is termed as repolarization.

25. PROPAGATION OF AN ACTION POTENTIAL
When an action potential travels down an axon, each successive portion of the axon undergoes a depolarization and then a repolarization.
As soon as an action potential has moved on the previous portion of an axon undergoes a refractory period during which the Na+ gates are unable to open. This ensures that the action potential does not move backwards and instead always moves down an axon.
In myelinated axons, the gated ion channels that produce an action potential are concentrated at the nodes of ranvier. Since ion exchange occurs only at the nodes, the AP travels faster in myelinated axons. This is called saltatory conduction, meaning the AP ‘jumps’ from nodes to nodes.

26. This propagation of AP along a nerve axon constitutes the nerve impulse. (certain local anesthetic drugs such as those use by dentist decrease membrane permeability to Na+. such a drug in the fluid surrounding an axon interrupt impulses from passing through the affected region and reaching the brain, preventing sensation of touch and pain).
The speed of impulse conduction depends on
The diameter of the neurone. The larger the diameter, the faster the conduction.
Whether the axon is myelinated or unmyelinated.

27. SYNAPSE
Nerve impulses travel along complex nerve pathways. The junction between any two communicating neurones is called synapse. However, the neurones at a synapse are not in direct physical contact. They are separated by a gap called a synaptic cleft.

28. SYNAPTIC TRANSMISSION
When you receive a call, the person making the call is the sender, and you are the receiver. Similarly, the neurone carrying impulse into the synapse is the sender or presynaptic neurone. The neurone receiving the input at the synapse is the receiver or postsynaptic neurone. The process of crossing the synaptic cleft with this message is called synaptic transmission.

29. Transmission across a synapse is carried out by biochemicals called neurotransmitters which are stored at synaptic vesicles in the axon bulbs. When an impulse reaches a synaptic knob some of the synaptic vesicles release neurotransmitters.
The neurotransmitter diffuses across the synaptic cleft and reacts with specific receptors on the postsynaptic neurone membrane. Neurotransmitters that increase postsynaptic membrane permeability of Na ions will bring postsynaptic membrane closer to threshold and may trigger nerve impulses. Such neurotransmitter is excitatory. E.g. acetylcholine and norepineprine.

30. Others make it less likely that threshold will be reached
Others make it less likely that threshold will be reached. This action is called inhibitory, because it lessons the chance that a nerve impulse will occur. E.gs of some neurotransmitters are acetylcholine, nor epinephrine, dopamine, serotonine, gamma amino butyric acid (GABA), etc.

32. THE CENTRAL NERVOUS SYSTEM (CNS)
The central nervous system consists of the brain and the spinal cord. Both the brain and the spinal cord are protected by bones and meninges.
MENINGES
Bones, membranes and fluid surround the organs of the CNS. The brain lies within the cranial cavity of the skull, and the spinal cord occupies the vertebral column. Layered membranes called meninges lie between these bony coverings and the soft tissues of the CNS, protecting the brain and spinal cord. The meninges have 3 layers namely dura mater, arachnoid mater and pia mater.

33. Dura mater
This is the outermost layer of the meninges. It is composed of tough, white, fibrous connective tissue and contains many blood vessels and nerves.
It attaches to the inside of the cranial cavity and forms the internal periosteum of the surrounding skull bones. In some regions, the dura mater extends inward between lobes of the brain and forms partitions that support and protect these parts.
It continues into the vertebra canal as a strong tubular sheath that surrounds the spinal cord .It terminates as a blind sac below the end of the cord. The membrane around the spinal cord is not attached directly to the vertebrae but separated by an epidural space which lies between the dura sheath and bony walls. This space contains loose connective and adipose tissues, which pad the spinal cord

34. Arachnoid mater
It is a thin web-like membrane without blood vessels that lies between the dura mater and the pia mater. It spreads over the brain and the spinal cord but does not dip into the grooves and depressions on their surfaces. Between the arachnoid and pia maters is a subarachnoid space that contains the clear watery cerebrospinal fluid (CSF). It is separated from the dura mater by the subdural space. 
Pia mater
The pia mater is very thin and contains many nerves and blood vessels that nourish underlying cells of the brain and spinal cord. This layer hugs the surface of these organs and follows their irregular contours, passing over high areas and dipping into depressions.

35. Ventricles and CSF
Within the cerebral hemispheres and the brainstem is a series of interconnected cavities called ventricles. These spaces contain CSF. The largest ventricles are the lateral ventricles (first and second ventricles) which extend into the cerebral hemispheres and occupy portions of the frontal, temporal and occipital lobes.
A narrow space that constitutes the third ventricle is in the midline of the brain, beneath the corpus callosum. This ventricle communicates with the lateral ventricles through openings called interventricular foramina.

36. Tiny, reddish, cauliflower- like masses of specialized capillaries from the pia mater called choroid plexuses secrete CSF. These structures project into the ventricles.
Most of the CSF arises from the lateral ventricles. From there, it circulates slowly into the third and fourth ventricles and into the central canal of the spinal cord.

37. The fourth ventricle is in the brainstem just anterior to the cerebellum. A narrow canal, cerebral aqueduct connects it to the third ventricle.
The fourth ventricle is continues with the central canal of the spinal cord and has openings in its roof that leads into the subarachnoid space of the meninges.

38. CSF also enters the subarachnoid space of the meninges through the wall of the fourth ventricle near the cerebellum and completes its circuit by being reabsorbed into the blood.
CSF completely surrounds the brain and the spinal cord. In effect, these organs float in the fluid.

39. Constituents of CSF
Water
Glucose
Mineral salts
Plasma proteins: small amounts of albumin and globulin.
Urea
Creatinine in small amounts

40. Functions of CSF
It supports and protects the brain and the spinal cord
It maintains a uniform pressure around these delicate structures
It keeps the brain and the spinal cord moist and there may be interchange of substances between CSF and nerve cells, such as nutrients and waste products.

41. Functions of CSF
4. It acts as a cushion and shock absorber between the brain and the cranial bones as well as the spinal cord and the vertebral column.
5. It aids in diagnosis and in the administration of drugs

42. THE SPINAL CORD
The spinal cord is a slender nerve column that extends from the base of the brain through a large opening in the skull called the foramen magnum and into the vertebral canal.
The cord tapers to a point and terminates near the intervertebral disc that separates the first and second lumbar vertebrae.
The spinal cord is approximately 45cm long and is about the thickness of the little finger.

44. Structure
The spinal cord consists of 31 segments, each of which gives rise to a pair of spinal nerves. These nerves branch to various body parts and connect them with the CNS.
In the neck region, a thickening in the cord called the cervical enlargement supplies nerves to the upper limbs. A similar thickening in the lower back, the lumber enlargement gives off nerves to the lower limbs.

45. Two grooves, a deep anterior median fissure and a shallow posterior median sulcus, extend the length of the spinal cord, dividing it into right and left halves.
A cross section of the cord reveals a core of gray matter within white matter.

47. The pattern of the gray matter roughly resembles a butterfly with its wings spread or the letter H. The upper and lower wings of gray matter are called the posterior(dorsal) and anterior(anterior) horns respectively.
Between them on either side in the thoracic and upper lumbar segments is a protrusion of gray matter called the lateral horn.

48. Gray matter divides the white matter of the spinal cord into 3 regions on each side- anterior, lateral and posterior funiculi.
A horizontal bar of gray matter in the middle of the cord, the gray commissure, connects the wings of the gray matter on the right and left sides. This bar surrounds the central canal which contains CSF.

49. The nerve tracts of the spinal cord consist of axons that provide a two way communication system between the brain and the body parts outside the nervous system.
Tracts that carry sensory information to the brain are called ascending tracts.
Those that conduct motor impulses from the brain to muscles and glands are called descending tracts.

50. Functions of the spinal cord.
The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord.
Example when someone touches your hands sensory receptors generate nerve impulses that pass through sensory fibers to the spinal cord and up ascending tracts to the brain.  

51. When we voluntarily move our limbs motor impulses originating in the brain pass down descending tracts to the spinal cord and out to our muscles by way of motor fibers.
2. The spinal cord is also the center for thousands of reflex arcs.

52. THE BRAIN
The brain constitutes about 1/50th of the body weight and lies within the cranial cavity.
It is composed of about 100 billion multi-polar neurons which communicate with one another and with neurons in other parts of the nervous system. The brain can be divided into four major portions
The cerebrum
The diencephalon
The brain stem
Cerebellum

54. THE CEREBRUM
It is the largest potion of the brain in human. Just as the human body has two halves so does the cerebrum. These halves are called right and left cerebral hemispheres.
A deep bridge of nerve fibers connects the two hemispheres (corpus callosum) and a layer of dura matter (falx cerebrum) separates them.
A deep groove called the longitudinal fissure divides the left and right hemispheres and shallow grooves called sulci divide each hemisphere into lobes.

55. The surface of the cerebrum has many ridges of convolutions (gyri) separated by grooves.
A thin layer of gray matter called the cerebral cortex is the outermost portion of the cerebrum.
The cerebral cortex is the region of the brain that accounts for sensation, voluntary movement and all the thought processes we associate with consciousness.

56. The lobes of the cerebral hemispheres are named after the skull bones they underlie. They include:
Frontal lobe: the fontal lobe forms the anterior portion of each cerebral hemisphere. It is bordered posteriorly by a central sulcus which extends from the longitudinal fissure at a right angle, and inferiorly by a lateral sulcus which extends from the under surface of the brain along its sides.
Parietal lobe: it is posterior to the frontal lobe and separated from it by the central sulcus.
Temporal lobe: it lies below the frontal and parietal lobes and it is separated from them by the lateral sulcus.

57. Occipital lobe: It forms the posterior portion of each cerebral hemisphere and it is separated from the cerebellum by a shelf-like extension of dura matter (tentorium cerebella). The boundary between occipital lobe and the parietal and the temporal lobe is not distinct.

59. FUNCTIONS OF THE CEREBRUM.
The cerebrum provides higher brain functions. It has centers for interpreting sensory impulses arising from sensory organs and center for interpreting voluntary muscular movement.
The cerebrum stores the information that comprises memory and utilizes it to reason.
Intelligence and personality also stem from sensory cerebral activities.

61. FUNCTIONAL REGIONS OF THE CEREBRAL CORTEX.
Specific regions of the cerebral cortex perform certain specific functions.
Although functions overlap among regions the cortex is divided into motor, sensory and association areas.

62. Motor area
The primary motor area of the cerebral cortex lies in the frontal lobe just in front of the cerebral sulcus. Voluntary commands for skeletal muscles begin in the primary motor area.
Most of the axons in the tract crossover from one side of the brain to the other side of the brain stem. As a result, the motor area at the right cerebral hemisphere generally controls skeletal muscles or the left side of the body and vise versa.

63. In addition to the primary motor area, certain other regions of the frontal lobe affect motor function. For example, a region called Broca’s area (motor speech area) is just anterior the primary motor area and superior to the lateral sulcus. It coordinates the complex muscular actions of the mouth, tongue, and larynx that make speech possible.

64. Above the Broca’s area a region called the frontal eye field which controls voluntary eye and eyelid movements.
The pre-motor area controls the muscular movement of the hands and fingers that make skills such as writing possible.

65. Sensory areas
Sensory areas located in several lobes the cerebrum interpret impulses arrives from sensory receptors, producing feeling or sensations. For example sensations from all parts of the skin (cutaneous senses) arise in the anterior portion of the parietal lobe along the central sulcus.
The posterior portion of the occipital lobe affects vision (visual area) and temporal lobe contains the center for hearing (auditory area).

66. The sensory areas for taste are located at the base of the central sulci along the lateral sulci and the sense of smell arises from the center deep within the cerebrum.
Like the motor fibers, sensory fibers cross over either in the spinal cord or in the brain stem.
Thus the centers in the right cerebral hemisphere interpret impulses originating from the left side of the body and vise versa

67. Association areas
They are neither primarily sensory nor motor. They connect with one another and with other brain structures.
These areas analyses and interpret sensory experiences and oversee memory, reasoning, verbalizing judgment and emotion.
Association areas occupy the anterior portions of the frontal lobes and are wide spread in the lateral portion of the parietal, temporal and occipital lobes.

68. The parietal, temporal and occipital association areas meet near the posterior ends of the lateral sulcus.
This important region is called the general interpretative area, and it plays the primary role in complex thought processing.

69. DIENCEPHALON
It is located between the cerebral hemispheres and above the mid brain. It surrounds the third ventricle and it is composed largely of gray matter.
The hypothalamus, thalamus, optic chiasma, Infundibulum, pituitary glands, mammilary bodies and the pineal gland form the diencephalon.

70. The thalamus is a central relay station for sensory impulses ascending from other parts of the nervous system to the cerebral cortex.
It receives all sensory impulses except sense of smell and channels them to the appropriate region of the cortex for interpretation.

71. The hypothalamus forms the floor of the third ventricle and it is the integrating center that helps maintain homeostasis by regulating:
Body temperature
Water and electrolyte balance
Control of hunger and thirst
Sleep and wakefulness
Production of neurosecretory substances that stimulates the pituitary gland to secrete hormones.
Heart rate and arterial blood pressure.

72. THE BRAIN STEM
The brain cell is a bundle of nervous system that connects the cerebrum to the spinal cord. It includes the mid- brain, the Pons and the medulla oblongata.
Mid brain
The mid brain acts as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum.
It also has reflex centers for visual, auditory and tactile responses.

73. Pons
The Pons is a rounded bulge on the underside of the brain stem where it separates the mid-brain from the medulla oblongata.
The Pons contains bundles of axons travelling between the cerebellum and the rest of the CNS.
It also functions with the medulla oblongata to regulate breathing rate and has reflex centers concerned with head movement in responds to visual and auditory stimuli.

74. Medulla oblongata
It extends from the Pons to the foramen magnum of the skull.
It contains a number of reflex centers for regulating heart beat, breathing and vasoconstriction.
It also contains the reflex centers for vomiting, coughing, sneezing, hiccupping and swallowing.

76. Reticular formation
This is a complex network of nuclei (masses of gray matter) and fibers that extend the length of the brain stem.
When sensory impulses reach the reticular formation it responds by activating the cerebral cortex into a state of wakefulness.

77. Without this arousal, the cortex remains unaware of stimulation and cannot interpret sensory information or carry on thought processes.
Decreased activity in the reticular formation results in sleep.
If the RF is injured so that it cannot function, the person remains unconscious and cannot be aroused even with strong stimulation (comatose state).

78. CEREBELLUM
The cerebellum is a large mass of tissue located below the occipital lobe of the cerebrum and posterior to the Pons and medulla oblongata.
It consists of two lateral hemispheres partially separated by a layer of dura matter (falx cerebelli) and connected in the midline by a structure called the vermis. Like the cerebrum, the cerebellum is composed primarily of white matter with a thin layer of gray matter, the cerebellar cortex on its surface.

79. The cerebellum is a reflex center for integrating sensory information concerning the position of the body parts and for coordinating complex skeletal movements.
It also helps maintain posture.
Damage in the cerebellar cortex results in tremors, inaccurate movements of voluntary muscles, loss of tone and loss of equilibrium.

80. PERIPHERAL NERVOUS SYSTEM (PNS)
The PNS consists of nerves that branch out of the CNS and connects it to other body parts.
It includes the cranial nerves, which arise from the brain and spinal nerves which arise from the spinal cord.

81. The PNS can also be subdivided into the somatic and the autonomic nervous system. Generally the somatic nervous system consists of the cranial and spinal nerves fibers that connect the CNS to the skin and skeletal muscles; it oversees conscious activities.
The autonomic nervous system includes fibers that connect the CNS to viscera such as the heart, stomach, intestines and glands, it controls unconscious activities.

82. Cranial Nerves
Twelve pairs of cranial nerves arise from the underside of the brain. Except for the first pair, which begins within the cerebrum, these nerves originate from the brainstem.
They pass from their sites of origin through the foramina of the skull and lead to parts of the head, neck and trunk.

83. Most of the cranial nerves are mixed nerves, but some of those associated with special senses, such as smell and vision contain only sensory fibers.
Other cranial nerves that affect muscles and glands are composed primarily of motor fibers. The twelve pairs of cranial nerves are:

86. Olfactory nerves (sensory): transmit impulses associated with sense of smell.
Optic nerves (sensory): sense of vision.
Oculomotor nerves (motor): muscles that raise eyelids, moves the eye. Arise from the midbrain.
Trochlear nerves (motor): transmits impulses that move the eye. It is from the midbrain and are the smallest cranial nerves.

87. V. Trigeminal nerves (mixed): 3 divisions and arise from the pons
V. Trigeminal nerves (mixed): 3 divisions and arise from the pons. Largest cranial nerves.
Ophthalmic division transmits impulses from the eye, tear gland, upper eyelid,etc
Maxillary division transmits impulses from the upper teeth, upper gum, upper lip, skin of the face.
Mandibular division transmits impulses from the skin of the jaw, lower teeth, lower gum, and lower lips.

88. VI. Abducens (motor): moves the eye. Arise from the pons.
VII. Facial (mixed): motor fibers transmit impulses to muscles of facial expression. Sensory fibers are associated with taste. From the pons.
VIII. Vestibulocochlear (sensory): from the medulla oblongata.
Vestibule is involved with equilibrium
Cochlear is concerned with the sense of hearing

89. IX. Glossopharyngeal nerves (mixed): motor fibers transmit impulses to muscles of the pharynx, used in swallowing and to salivary glands. Sensory fibers transmit from the pharynx, tonsils, posterior tongue and carotid arteries. From the medulla oblongata.
X. Vagus nerves (mixed): sensory transmit impulses from the esophagus, pharynx, larynx. Somatic motor transmit impulses to muscles associated with speech, heart. From the medulla oblongata.

90. XI. Accessory (motor): cranial branch transmits impulses to soft palate, pharynx, and larynx. Spinal branch transmit impulses to muscles of the neck and back. From the medulla oblongata.
XII. Hypoglossal (motor): transmits impulses to muscles that move the tongue. From the medulla oblongata.

91. Spinal Nerves Thirty one pairs of spinal nerves originate from the spinal cord. They are mixed nerves that provide two way communications between the spinal cord and parts of the upper and lower limbs, neck and trunk. Spinal nerves are not named individually but are grouped according to the level at which they arise. Each nerve is numbered in sequence.

92. There are 8 pairs of cervical nerves (C1 to C8), 12 pairs of thoracic nerves (T1 to T12), 5 pairs of lumbar nerves (L1 to L5), 5 pairs of sacral nerves (S1 to S5) and a pair coccygeal nerve (Co).
The adult spinal cord ends at the level between the first and second lumbar vertebrae. The lumbar, sacral and coccygeal nerves descend beyond the end of the cord, forming a structure called cauda equine (horse’s tail).

93. Except in the thoracic region, the main portion of the spinal nerves combine to form complex network called plexuses instead of continuing directly to peripheral body parts.
There are 3 main plexuses namely,
cervical plexuses (C1 to C4)
brachial plexuses (C5 toT1)
lumbosacral plexuses (T12 to S5).