The Nervous System.

The Nervous System

Introduction Organs of the nervous system are divided into the Central (CNS) and the Peripheral (PNS) nervous systems. These structures provide sensory, integrative, and motor functions. Nervous tissue includes neurons, which are the structural and functional units of the nervous system, and neuroglial cells.

Introduction Sensory Functions derive from sensory receptors at the end of peripheral neurons. Receptors gather information by detecting changes inside and outside the body and then convert the info into nerve impulses, which are transmitted over peripheral nerves to the CNS.

Introduction 2. Integrative functions are receiving signals and bringing them together, creating sensations, adding to memory, or helping to produce thoughts that translate sensations into perceptions.

Introduction 3. Motor functions employ peripheral neurons, which carry impulses from the CNS to responsive structures called effectors (muscles and glands that secrete when stimulated).

Neurons: Basic Unit of the Nervous System

Neuron Structure Cell Body (Soma)– consists of granular cytoplasm, cell membrane, organelles, and a network of fine threads called neurofibrils, which extend into nerve fibers

Neuron Structure Nerve Fibers – extend from the cell body

Neuron Structure Dendrites – one neuron may have many dendrites; short and highly branched; together with the membrane, dendrites are the neuron’s main receptive surfaces with which fibers from other neurons communicate

Neuron Structure Axons – one neuron has only one axon; arises from slight elevations of the cell body; begins as a single fiber but may give off side branches; near its end it may have fine extensions that contact the receptive surfaces of other cells

Neuron Structure Schwann cells – neuroglial cells that enclose large axons forming myelin sheaths that wind tightly around the axon; portions of the Schwann cells that contain most of the cytoplasm and the nuclei remain outside the myelin sheath and make up the nuerilemma (neurilemmal sheath); narrow gaps in the myelin sheath between Schwann cells are called nodes of Ranvier

Neuron Structure CNS – myelinated nerve fibers are also found in the central nervous system; myelinated fibers appear white, and masses of such fibers form white matter in the CNS; unmyelinted nerve fibers and neuron cell bodies form gray matter within the CNS

Types of Neuron and Neuroglial Cells

Classification of Neurons: Structural Differences
Bipolar Neurons – cell body has two nerve fibers one arising from each end; one is an axon and the other is a dendrite; located within specialized parts of the eye, nose and ears

Unipolar Neurons – single nerve fiber that extends from the cell body then divides into two branches; one connecting to a peripheral body part and functioning as a dendrite, and the other entering the brain or spinal cord and functioning as an axon; some cell bodies gather in specialized masses of nervous tissue called ganglia(located outside the brain or spinal cord)

Multipolar Neurons – have many nerve fibers arising from their cell bodies; only one fiber is an axon and the rest are dendrites; neurons which lie within the brain or spinal cord

Classification of Neurons: Functional Differences
Sensory Neurons (afferent neurons) – carry impulses from peripheral body parts into the brain or spinal cord; most are unipolar, but some are bipolar

Interneurons (internuncial or association neurons) – lie within the brain and spinal cord; multipolar and link other neurons; transmit impulses from one part of the brain or spinal cord to another; direct incoming sensory impulses to appropriate parts for processing and interpreting

Motor Neurons (efferent neurons) – multipolar and carry impulses out of the brain or spinal cord to effectors; stimulate muscles to contract or glands to secrete

Classification of Neuroglial Cells:
Neuroglial cells fill spaces, provide structural frameworks, produce myelin, and carry on phagocytosis. Within the PNS neuroglial cells include Schwann cells; in the CNS they greatly outnumber neurons and are of the following types:

Microglial Cells – scattered throughout; support neurons and phagocytize bacterial cells and cellular debris

Astrocytes – found between neurons and blood vessels; provide structural support, join parts by numerous cellular processes, help regulate the concentrations of nutrients within tissue; form scar tissue that fills spaces following injury to the CNS

Ependymal Cells – form an epithelial like membrane that covers specialized brain parts and forms the linings that enclose spaces within the brain and spinal cord

Cell Membrane Potential
A cell membrane is usually polarized as a result of unequal ion distribution.

Distribution of Ions a. Ion distribution is due to pores and channels in the membranes that allow passages of some ions but not others b. Potassium ions (K+) pass more easily through cell membranes than do Sodium ions (Na+)

Resting Potential a. a high concentration of sodium ions is on the outside of a membrane, and a high concentration of potassium ions is on the inside of the cell. b. Many negatively charged ions are inside a cell. c. In a resting cell, more positive ions leave than enter, so the outside of the cell membrane develops a positive charge, while the inside develops a negative charge.

Potential Changes a. Stimulation of a membrane affects the membrane’s resting potential. b. When its resting potential becomes more positive, a membrane becomes depolarized. c. Potential changes are subject to summation. d. Achieving threshold potential triggers an action potential.

Action Potential a. At threshold, sodium channels open, and sodium ions diffuse inward, depolarizing the membrane. b. About the same time, potassium channels open, and potassium ions diffuse outward, repolarizing the membrane c. This rapid change in potential is an action potential. d. Many action potentials can occur before active transport re-establishes the resting potential.

Nerve Impulses: A wave of action potentials is a nerve impulse.
Impulse Conduction Unmyelinated fibers conduct impulses over the entire surface of the nerve. 2. Myelinated fibers conduct impulses more rapidly because the impulse jumps between the nodes of Ranvier. 3. Nerves with large diameters conduct impulses faster than those with small diameters.

Nerve Impulses All-or-None Response
A nerve impulse is conducted in an all-or-none manner when a stimulus of threshold intensity is applied to a fiber. 2. All the impulses conducted on a fiber are of the same strength.

The Synapse – A synapse is the junction between two neurons.
Synaptic Transmission 1. Impulses usually travel from a dendrite to a cell body, then along the axon to a synapse. 2. Axons have synaptic knobs at their ends, which secrete neurotransmitters. 3. A neurotransmitter is released when a nerve impulse reaches the end of an axon. 4. A neurotransmitter reaching the nerve fiber on the distal side of the synaptic cleft triggers a nerve impulse.

The Synapse

The Synapse Excitatory and Inhibitory Actions
Neurotransmitters that trigger nerve impulses are excitatory. Those that inhibit impulses are inhibitory. 2. The net effect of synaptic knobs communicating with a neuron depends on which knobs are activated from moment to moment.

The Synapse Neurotransmitters
The nervous system produces many different neurotransmitters, such as acetylcholine, monoamines, amino acids, and peptides. 2. A synaptic knob releases neurotransmitters when an action potential increases membrane permeability to calcium ions. 3. After being released, neurotransmitters are decomposed or removed from synaptic clefts.

Types of Nerves Nerves are cordlike bundles of nerve fibers held together by layers of connective tissue.

Types of Nerves 1. Sensory Nerves – conduct impulses into the brain or spinal cord 2. Motor Nerves – carry impulses to muscles or glands 3. Mixed nerves – include both sensory and motor fibers

Nerve Pathways A nerve pathway is a route an impulse follows through the nervous sytem.

Nerve Pathways Reflex arc – usually includes a sensory neuron, a reflex center composed of an interneuron, and a motor neuron

Reflex Behavior 1. Reflexes are autonomic, subconscious responses to changes (stimuli) within or outside the body. 2. Reflexes help maintain homeostasis by controlling may involuntary processes. 3. Reflexes carry out autonomic actions of swallowing, sneezing, coughing, and vomiting. 4. The knee-jerk reflex (patellar tendon reflex) employs two neurons (sensory and motor). 5. Withdrawal reflexes are protective. Employs all three types of nerves.

Meninges Meninges are membranes that lie between the bones and soft tissues of the cranial cavity and vertebral canal. They protect the brain and spinal cord

Meninges They consists of three layers:
1. Dura Mater – outermost layer 2. Arachnoid Mater – located between the dura and pia mater a. Subarachnoid space – lies between the arachnoid and pia mater and contains the clear watery cerebrospinal fluid (CFS) 3. Pia Mater – very thin and contains nerves and blood vessels that nourish underlying cells of the brain and spinal cord; hugs the surface of these organs following their irregular contours, passing over high areas and dipping into depressions

Spinal Cord The spinal cord is a nerve column that extends from the brain into the vertebral canal.

Structure of the Spinal Cord
The spinal cord is composed of thirty-one segments, each of which gives rise to a pair of spinal nerves. The spinal cord has a cervical enlargement, which gives off nerves to the upper limbs, and a lumbar enlargement, which gives off nerves to the lower limbs.

Spinal Nerves

Structure of the Spinal Cord
Two grooves, a deep anterior fissure and a shallow posterior median sulcus, extend the length of the spinal cord, dividing it into right and left halves. It has a central core of gray matter within white matter. The white matter is composed of bundles of myelinated nerve fibers that comprise major nerve pathways called nerve tracts.

Functions of the Spinal Cord
Conduction of Nerve Impulses – provides a two-way communication system between the brain and body parts. Ascending tracts carry sensory information to the brain and descending tracts conduct motor impulses from the brain to muscles and glands. Center for Spinal Reflexes

The Brain

Structures of the Cerebrum
Cerebral Hemisphere – 2 large masses which are essentially mirror images of each other connected by a deep bridge of nerve fibers called the corpus callosum; the surface has many convolutions (ridges) separated by grooves (shallow groove is called a sulcus and a deep groove is called a fissure)

The lobes of the cerebral hemisphere are named after the skull bones they underlie:
Frontal Lobe Parietal Lobe Temporal Lobe Occipital Lobe

Structures of the Cerebrum

Cerebral Cortex thin layer of gray matter that forms the outermost portion of the cerebrum; contains nearly 75% of all the neuron cell bodies in the nervous system

Mass of White Matter lies just beneath the cerebral cortex and makes up the bulk of the cerebrum; bundles of myelinated fibers

Functions of the Cerebrum

Functional Regions of the Cerebral Cortex
Primary Motor Areas – lie in the frontal lobes; fibers cross over in the brain stem from one side of the brain to the other (right CH motor area generally controls skeletal muscles on the left side of the body and vise versa) motor speech area frontal eye field

Sensory Areas – located in several lobes a. cutaneous senses – sensations of the skin b. visual area c. auditory area d. taste area e. smell area

Association Area – neither primarily sensory or motor; analyzes and interprets sensory experiences and oversees memory, reasoning, verbalizing, judgment, and emotion

General Interpretive Area – complex thought processing

Hemisphere Dominance Although both cerebral hemispheres participate in basic functions, in most people, one side of the cerebrum is the dominant hemisphere, controlling other functions.

Hemisphere Dominance In over 90% of the population, the left hemisphere is dominant for language-related activities of speech, writing, reading, and for complex intellectual functions requiring verbal, analytical, and computational skills.

Hemisphere Dominance In addition to carrying on basic functions, the non-dominant hemisphere specializes in nonverbal functions, such as motor tasks that require orientation of body in space, understanding, and interpreting musical patterns, and nonverbal visual experiences, as well as emotional and intuitive thinking.

Cerebrospinal Fluid Cerebrospinal Fluid is secreted by capillaries from the pia mater. It completely surrounds the brain and spinal cord. These organs float in the fluid, which supports and protects them. It also provides a pathway to the blood for waste

Diencephalon The diencephalon is located between the cerebral hemispheres and above the midbrain. It is largely composed of gray matter

Diencephalon Thalamus – relay station for sensory impulses (except smell); produces a general awareness of certain sensations, such as pain, touch, and temperature

Diencephalon Hypothalamus – below thalamus; maintains homeostasis by regulating a variety of visceral activities and by linking the nervous and endocrine systems; regulates: heart rate and arterial blood pressure body temperature water and electrolyte balance control of hunger and body weight control of movements and glandular secretions of stomach and intestines production of neurosecretory substances that stimulate the pituitary gland to secrete hormones sleep and wakefulness

Hypothalamus

Diencephalon Limbic System – controls emotional experiences and expression; can modify the way a person acts by producing such feelings as fear, anger, pleasure, and sorrow; recognizes upsets in a person’s physical and psychological condition that might threaten life; guides a person into behavior that is likely to increase the chance of survival

Limbic System

Other Structures of the Diencephalon
1. Optic Tract Optic Chiasma 2. infundibulum – structures in which the pituitary gland is attached 3. pituitary gland 4. olfactory bulbs 5. pineal gland – structure that secretes melatonin, which affects the sleep cycle; the darker it is the more melatonin is released, the lighter it is the less melatonin is released

optic tracts and optic chiasma

infundibulum – structures in which the pituitary gland is attached

pituitary gland

olfactory bulbs

pineal gland structure that secretes melatonin, which affects the sleep cycle; the darker it is the more melatonin is released, the lighter it is the less melatonin is released

Brain Stem a bundle of nerve tissue that connects the cerebrum to the spinal cord

Midbrain joins lower parts of the brain stem and spinal cord with higher parts of the brain; contains centers for certain visual and auditory reflexes

Pons rounded bulges on the underside of the brain stem; transmits impulses to and from the cerebrum and medulla oblongata and the cerebrum and cerebellum; relays messages from the PNS to high brain centers and functions with the medulla oblongata in regulating the rate and depth of breathing

Medulla Oblongata All descending and ascending nerve fibers pass through the medulla oblongata. It is composed of gray matter surrounded by white matter and contains contains centers for controlling visceral activities: cardiac center – alters heart rate b. vasomotor center – certain cells initiate impulses which stimulate blood vessels to contract (vasoconstriction) elevating blood pressure; other cells have the opposite affect – dilating blood vessels (vasodilation) dropping blood pressure c. respiratory center – acts with centers in the pons to regulate the rate, rhythm, and depth of breathing

Medulla Oblongata

Reticular Formation (reticular activating system)
The reticular formation extends from the upper portion of the spinal cord into the diencephalon and is connected to all ascending and descending fiber tracts. When sensory impulses are received it activates the cerebral cortex into wakefulness. Without this arousal, the cortex remains unaware of stimulation and cannot interpret information or carry out thought processes. Decreased activity results in sleep. Injury to it causes a person to be unconscious and cannot be aroused, even with strong stimulation (comatose state).

Cerebellum large mass located below the occipital lobes and posterior to the pons and medulla oblongata; two hemispheres composed largely of white matter surrounded by a thin layer of gray matter;

Cerebellum communicates with other parts of the CNS by means of three pairs of nerve tracts called cerebellar peduncles: a. inferior peduncle – brings sensory information concerning the position of the limbs, joints, and other body parts to the cerebellum b. middle peduncle – transmits signals from the cerebral cortex to the cerebellum concerning the desired positions of the above mentioned parts; after integrating and analyzing this information the cerebellum sends correcting information via the superior peduncle

Cerebellum

Cerebellum Thus, the cerebellum is a reflex center for integrating sensory information concerning position of the body parts and for coordinating complex skeletal muscle movements. Damage is likely to result in tremors, inaccurate movements of voluntary muscles, loss of muscle tone, a reeling walk, and loss of equilibrium.

Peripheral Nervous System

Somatic Nervous System
The somatic nervous system consists of the cranial and spinal nerve fibers that connect the CNS to the skin and skeletal muscles. It oversees conscious activities.

Autonomic Nervous System
The autonomic nervous system consists of sensory neurons and motor neurons that run between the central nervous system (especially the hypothalamus and medulla oblongata) and various internal organs such as the: heart lungs viscera glands (both exocrine and endocrine)

The autonomic nervous system is the portion of the PNS that functions independently (autonomously) and continuously without conscious effort. It controls visceral functions by regulating the actions of smooth muscles, cardiac muscles, and glands. 2. It regulates heart rate, blood pressure, breathing rate, body temperature, and other visceral activities that maintain homeostasis. 3. Portions respond to emotional stress and prepare the body to meet demands of strenuous physical activity

General Characteristics: regulated by reflexes typically, peripheral nerve fibers lead to ganglia outside the CNS where they are integrated and relayed back to viscera (muscles and glands) that respond by contracting, releasing secretions, or being inhibited provides the autonomic system with a degree of independence from the brain and spinal cord includes two divisions:

The autonomic nervous system includes two divisions: Sympathetic division – prepares the body for energy-expending, stressful, or emergency situations Parasympathetic division – most active during ordinary, restful conditions; counterbalances the effects of the sympathetic division and restores the body to a resting state following a stressful experience

Sympathetic division The preganglionic motor neurons of the sympathetic system (shown in black) arise in the spinal cord. They pass into sympathetic ganglia which are organized into two chains that run parallel to and on either side of the spinal cord.

Sympathetic division The preganglionic neuron may do one of three things in the sympathetic ganglion: synapse with postganglionic neurons (shown in white) which then reenter the spinal nerve and ultimately pass out to the sweat glands and the walls of blood vessels near the surface of the body. pass up or down the sympathetic chain and finally synapse with postganglionic neurons in a higher or lower ganglion leave the ganglion by way of a cord leading to special ganglia (e.g. the solar plexus) in the viscera. Here it may synapse with postganglionic sympathetic neurons running to the smooth muscular walls of the viscera. However, some of these preganglionic neurons pass right on through this second ganglion and into the adrenal medulla. Here they synapse with the highly-modified postganglionic cells that make up the secretory portion of the adrenal medulla.

Sympathetic division The neurotransmitter of the preganglionic sympathetic neurons is acetylcholine (ACh). It stimulates action potentials in the postganglionic neurons. The neurotransmitter released by the postganglionic neurons is noradrenaline (also called norepinephrine). The action of noradrenaline on a particular gland or muscle is excitatory is some cases, inhibitory in others. (At excitatory terminals, ATP may be released along with noradrenaline.)

Sympathetic division The release of noradrenaline stimulates heartbeat
raises blood pressure dilates the pupils dilates the trachea and bronchi stimulates glycogenolysis — the conversion of liver glycogen into glucose shunts blood away from the skin and viscera to the skeletal muscles, brain, and heart inhibits peristalsis in the gastrointestinal (GI) tract inhibits contraction of the bladder and rectum and, at least in rats and mice, increases the number of AMPA receptors in the hippocampus and thus increases long-term potentiation (LTP).

Sympathetic division In short, stimulation of the sympathetic branch of the autonomic nervous system prepares the body for emergencies: for "fight or flight" (and, perhaps, enhances the memory of the event that triggered the response). Activation of the sympathetic system is quite general because a single preganglionic neuron usually synapses with many postganglionic neurons; the release of adrenaline from the adrenal medulla into the blood ensures that all the cells of the body will be exposed to sympathetic stimulation even if no postganglionic neurons reach them directly.

Parasympathetic Nervous System
The main nerves of the parasympathetic system are the tenth cranial nerves, the vagus nerves. They originate in the medulla oblongata. Other preganglionic parasympathetic neurons also extend from the brain as well as from the lower tip of the spinal cord.

Each preganglionic parasympathetic neuron synapses with just a few postganglionic neurons, which are located near — or in — the effector organ, a muscle or gland. Acetylcholine (ACh) is the neurotransmitter at all the pre- and many of the postganglionic neurons of the parasympathetic system. However, some of the postganglionic neurons release nitric oxide (NO) as their neurotransmitter.

Parasympathetic stimulation causes: slowing down of the heartbeat lowering of blood pressure constriction of the pupils increased blood flow to the skin and viscera peristalsis of the GI tract

In short, the parasympathetic system returns the body functions to normal after they have been altered by sympathetic stimulation. In times of danger, the sympathetic system prepares the body for violent activity. The parasympathetic system reverses these changes when the danger is over.

The vagus nerves also help keep inflammation under control. Inflammation stimulates nearby sensory neurons of the vagus. When these nerve impulses reach the medulla oblongata, they are relayed back along motor fibers to the inflamed area. The acetylcholine from the motor neurons suppresses the release of inflammatory cytokines, e.g., tumor necrosis factor (TNF), from macrophages in the inflamed tissue.

Although the autonomic nervous system is considered to be involuntary, this is not entirely true. A certain amount of conscious control can be exerted over it as has long been demonstrated by practitioners of Yoga and Zen Buddhism. During their periods of meditation, these people are clearly able to alter a number of autonomic functions including heart rate and the rate of oxygen consumption. These changes are not simply a reflection of decreased physical activity because they exceed the amount of change occurring during sleep or hypnosis.

Cranial Nerves 12 pairs arise from the underside of the brain; except for the first pair, which begins within the cerebrum lead to parts of the head, neck, and trunk most are mixed nerves, but some associated with smell and vision contain only sensory fibers some that control muscles and glands in this area are primarily motor fibers

Cranial Nerves

Nerves Type Function I Olfactory sensory olfaction (smell) II Optic
vision (Contain 38% of all the axons connecting to the brain.) III Oculomotor motor* eyelid and eyeball muscles IV Trochlear eyeball muscles V Trigamental mixed Sensory: facial and mouth sensation Motor: chewing VI Abducens eyeball movement VII Facial Sensory: taste Motor: facial muscles and salivary glands VIII Vestibulocochlear hearing and balance IX Glossopharyngeal Sensory: taste Motor: swallowing X Vagus main nerve of the parasympathetic nervous system (PNS) XI Accesory motor swallowing; moving head and shoulder XII Hypoglossal tongue muscles

Spinal Nerves 31 pairs originate from the spinal cord
All of the spinal nerves are "mixed"; that is, they contain both sensory and motor neurons. They provide two way communication between the spinal cord and parts of the upper and lower limbs, neck, and trunk.

Spinal Nerves Spinal nerves are grouped according to the level in which they arise: cervical nerves (C1-C8) – 8 pairs thoracic nerves (T1-T12) – 12 pairs lumbar nerves (L1-L5) – 5 pairs sacral nerves (S1-S5) – 5 pairs coccygeal nerve (C0) – one pair

Spinal Nerves The adult spinal cord ends at the level between the first and second lumbar vertebrae, so the lumbar, sacral, and coccygeal nerves descend beyond the end of the cord, forming a structure called the cauda equina (horse’s tail).

Spinal Nerves

The Nervous System.

Similar presentations

Presentation on theme: "The Nervous System."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

The Nervous System.

Similar presentations

Presentation on theme: "The Nervous System."— Presentation transcript:

Similar presentations

About project

Feedback