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 3rd

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 3rd 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 3rd

ventricle to 4th 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. 4th ventricle is posterior

4) Cerebellum

• Coordinates skeletal muscle activity, controls balance and equilibrium, monitors body position

Protection of the Brain1) Skull2) Meninges- 3 parts: Dura Mater- outside tough layer Arachnoid Mater- middle blood vessels Pia Mater- surface of the brain layer3) 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 1st 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