Nervous System- Anatomy

Central Nervous System Brain Spinal Cord (also includes 4 chambers in brain called ventricles)

Brain 1) Cerebral Hemispheres 2) Diencephalon 3) Brain Stem 4) Cerebellum

1) Cerebral Hemispheres Covered by ridges = gyri Ridges separated by grooves = sulci The hemispheres (right and left) Are separated by a single deep longitudinal fissure Other shallow fissures divide each hemisphere into lobes Lobes are named for the cranial bones over them

Ear to ear is the central fissure (sulci) Posterior to the central fissure in the parietal lobe is the somatic sensory area (post central gyri) Impulses that travel from sensory receptors are interpreted there Crossed pathways

Anterior to the central fissure in the frontal lobes is the primary motor area (Pre central gyri) Allows us to consciously move our skeletal muscles Major voluntary motor tract that descends to the spinal cord Crossed pathways

Areas in Cerebrum Impulses for special senses: Visual = posterior occipital Auditory = temporal lobe (lateral fissure) Olfactory = deep temporal lobe

Impulses for the special senses: Broca’s area = base of the pre- central gyrus located in left hemisphere only, gives ability to say words properly Speech Area = junction of temporal, parietal, and occipital lobes, allows understanding of words, spoken or read and response to them

Higher Reasoning = anterior frontal lobe Complex Memories = temporal and frontal lobes

Gray matter – of cerebral hemispheres contain the cell bodies of neurons White matter – of cerebral hemispheres is composed of fiber tracts which carry impulses to or from the cortex

Corpus callosum – a very large fiber tract that connects the cerebral hemispheres and allow left and right brain to communicate Basal nuclei or basal ganglia are buried within the white matter and help regulate voluntary motor activities

2) Diencephalon Interbrain: Thalamus- encloses the 3 rd ventricle, relay for sensory impulses

Hypothalamus- floor of diencephalon, autonomic center. Functions: regulates body temperature, water balance, and metabolism, contains the “limbic system” which is a center for many drives; thirst, appetite, sex, pleasure, -Regulates the pituitary gland, contains mammillary bodies

Epithalmus- forms the roof of the 3 rd ventricle, contains pineal body (endocrine gland), contains: Choroid plexus which forms CSF (cerebral spinal fluid)

3) Brain Stem Midbrain- extends from the mammillary bodies (in diencephalon) to the pons Cerebral aqueduct- connects 3 rd ventricle to 4 th ventricle Corpora Quadrigemina- four rounded protrusions – reflex centers for vision and hearing

Pons- just below midbrain, mostly fiber tracts, important for control of breathing Medulla Oblongata- most inferior part of brain stem, merges with spinal cord, mostly fiber tracts. Functions-controls heart rate, blood pressure, breathing, swallowing, vomiting. 4 th ventricle is posterior

4) Cerebellum Coordinates skeletal muscle activity, controls balance and equilibrium, monitors body position

Protection of the Brain 1)Skull 2)Meninges- 3 parts: Dura Mater- outside tough layer Arachnoid Mater- middle blood vessels Pia Mater- surface of the brain layer 3) Cerebral Spinal Fluid- CSF continuously formed by choroid plexus, cushions, protects, runs down central canal of the spinal cord

Problems of the Brain Concussion Contusion Hemorrhage CVA, aphasia, paralysis TIA Alzheimer’s disease Parkinson’s disease

Spinal Cord 17 inches from skull to L2 Reflex center and 2 way conduction pathway Central canal contains CSF

Gray Matter of Spinal Cord Dorsal Horns (posterior)- contains interneurons and sensory neurons; enter by dorsal root (ganglion) Ventral Horns (anterior)- contain motor neurons, (somatic voluntary), leave by the ventral root The dorsal and ventral roots fuse to form the spinal nerves

White Matter of Spinal Cord Myelinated fiber tracts, some run to other side of spinal cord, some run to higher centers All tracts in the anterior and lateral cord are motor All tracts in the posterior cord are sensory

Problems of the Spinal Cord Dorsal root damage- sensory damage = parasthesis Ventral root damage- motor damage = paralysis

Peripheral Nervous System Contains nerves: spinal and cranial A nerve is a bundle of neurons found outside the CNS Nerves are neurons bundled in connective tissue

Nerves are named like neurons: Carry to CNS= afferent Carry from CNS= efferent Carrying both sensory and motor= mixed (all spinal)

Cranial Nerves- 12 pair 1. olfactory- sensory 2. optic- sensory 3. oculomotor- motor 4. trochlear- motor 5. trigeminal- mixed 6. abducens- motor

7. facial- mixed 8. vestibulocochlear- sensory 9. glossopharyngeal- mixed 10. vagus- mixed 11. accessory- mostly motor 12. hypoglossal- mixed

Spinal Nerves – 31 pairs Formed from the fusion of the ventral and dorsal roots of the spinal cord Divides into dorsal and ventral rami Both types of rami contain both sensory and motor nerves, just go to different places

Dorsal rami are smaller and serve skin and muscle of posterior body trunk Ventral rami of T1- T12 form intercostal nerves All other ventral rami form plexuses which serve limbs, neck, and diaphragm

Two Divisions of the Peripheral Motor Nervous System Somatic Nervous System Autonomic Nervous System

Somatic Nervous System One neuron extends to skeletal muscle Voluntary

Autonomic Nervous System Involuntary, Automatic Motor control of cardiac muscle, smooth muscle, and glands Involves a chain of two motor neurons called: pre ganglion and post ganglion

Autonomic Nervous System has two arms: Parasympathetic- rest and digest / homeostasis Sympathetic- emergency; fight or flight

Both serve the same organ Each release different neurotransmitters Parasympathetic= cholinergic fibers Sympathetic= adrenergic fibers

Parasympathetic Pre-ganglion neuron secretes acetylcholine Post-ganglion neuron secretes acetylcholine

Sympathetic Pre- ganglion neuron secretes acetylcholine Post- ganglion neuron secretes epinepherine

Parasympathetic Rest and digest Continued homeostasis

Sympathetic Increased: heart rate, blood pressure and glucose Dilation of: bronchioles and blood vessels Close down digestive system Activate adrenal glands

Developmental problems Nervous system develops in the 1 st month of pregnancy Viruses, drugs, alcohol, smoking can affect embryo

Birth Defects Cerebral Palsy Hydrocephalus Anencephaly Spina bifida

Continued development Last to form = Hypothalamus Myelination continues through childhood Brain reaches maximum weight in the young adult (20s) New neural pathways can always be formed (learning)

Aging Problems Sympathetic system becomes inefficient in the elderly Arteriosclerosis and High Blood Pressure can cause decreased brain oxygen = senility < 5% senility at age 65 Boxers and chronic alcoholics show shrunken brains = senility

Reversible Senility Drug side effects, low blood pressure, depression, dehydration, and malnutrition can cause types of senility that will improve if the initial problem is corrected