Chapter 7
The Nervous
System
Divisions of the Nervous
System
• Principal Divisions
– Central Nervous System (CNS)
• Brain
• Spinal Cord
– Peripheral Nervous System (PNS)
• afferent (sensory)
– to CNS, sensory receptors
• efferent (motor) away from CNS
– somatic
» voluntary, skeletal muscle
» to effectors, muscle or glands
Divisions of the Nervous System
• Autonomic (involuntary) smooth
muscle, cardiac muscle, glands
–parasympathetic
»rest & digest
»Increased peristalsis
»Blood flow to digestive tract
–sympathetic
»flight or fight
»Increased heart and breathing
rate
Specialized Cells
• Neuroglia Cells ~ “glia” (glue)
– Support
– Insulate
– Protect
• astrocytes
• schwann cells
– PNS
– form myelin sheaths
Specialized Cells
• Neurons “ nerve cells”
– receive and transmit info
– cell body
• neuroplasm
• nucleus
• Nissl bodies - metabolism
– neuroplasm
– dendrites
• branching structures 100’s branches
• carry impulses toward cell body
Neuron Parts
• Axon
–
–
–
–
–
single process from cell body
carries impulses away from cell body
branch into axon terminals
have vesicles (sacs) w/ neurotransmitters
chemicals ---> synapse
• Myelin Sheath
–
–
–
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secreted by Schwann Cells
white fatty material around axon
Cushion & insulate
gray matter: unmyelinated
Specialized Cells
• Neurilemma
– only in PNS myelinated fibers
– Schwann cell cytoplasm
– Regeneration ( can repair)
– Nodes of Ranvier- indentations
allow for saltatory conduction
Specialized Cells
• Classification of Neurons
– Structure
• multipolar : most common
• bipolar: ears eyes
• unipolar: sensory
Nerve Impulses
• General
– Neural function involves:
• irritability: respond to stimuli
• conductivity: send impulses
• Reception
– stimulus
• dendrites on sensory receptors
– Neurotransmitter- chemicals
• Go across synapse to another neuron or
effector
Nerve Impulses
• Transmission
– Resting potential
• more Na+ outside K+ inside
– Action potential
•
•
•
•
threshold stimulus ---> Na+ gates open
Na+ go into the axon and K+ goes out
Reverses polarity
Summation- many subthresholds added
– Saltatory conduction ~ myelinated
• impulses jump from node to node
• 120 m/sec 10m/sec
• unmyelinated .5m/sec - 2m/sec
Nerve Impulses
• Transmission
– All or none law
• impulse is conducted along entire axon fully or not at all
• stronger stimulus ---> increase frequency of impulses
– Synapse
• neurotransmitters 100
–
–
–
–
–
–
Stored in synaptic vesicles
ACH
norepinephrine
serotonin
dopamine
endorphins
Nerve Impulses
• Reflex Arc
– rapid predictable involuntary response to
stimuli
– stimulus ---> sensory neuron --->
associative neuron ---> motor neuron --->
response
The Brain 3 lbs 100 billion cells
• Meninges
– three layers of connective tissue
• dura mater
– tough
– 2 layers
• arachnoid
– subaracnoid space
• pia mater
– little adhered to brain
• Cerebrospinal fluid - cushion
– in subarachnoid space
– watery broth - nutrients
• Blood brain barrier
– keeps neurons from toxins
• Urea protein drugs
Divisions of the Brain
• The Brain Stem
– blood pressure
– heart rate
– breathing
– swallowing & vomiting
• Medulla oblangata
– important reflexes- cardiac center
– autonomic
• Pons
– relay center (breathing)
• Midbrain
– reflex center
– turn ears and eye movement
Divisions of the Brain
• Interbrain (diencephalon)
– thalamus
• emotion, touch, temp.
• relay station, sense organs ---> cerebrum
– hypothalamus
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•
•
•
•
reflex activity
body temp., water balance
homeostasis
metabolism, appetite
emotions, pain pleasure
– epithalamus
• pineal gland- melatonin
• choroid plexus- forms CSF
Divisions of the Brain
• Cerebellum
– two hemispheres
– arbor vitae (white matter) inside gray
cortex
– balance
– muscle tone & coordination
Divisions of the Brain
• Cerebrum
– cerebral hemispheres
• separated by longitudinal fissure outer gray
cortex
• more surface area convolutions
– gyri - ridges
– sulci - grooves
– fissures - deeper grooves
– cerebral dominance
• right
– spatial, holistic, creativity
• left
– linguistic, analytical, logical
Divisions of the Brain
• Cerebrum
– corpus callosum
• band of neurons
• integrates & coordinates two hemispheres
– cerebral functions
•
•
•
•
•
•
conscious thought
voluntary movement
reasoning & emotions
speech
memory
intelligence
Divisions of the Brain
• Cerebrum
– lobes
• frontal
– prefrontal, intellect, personality, cognition,
problem solving, language, motor
• parietal
– sensory, temperature, touch
• occipital
– visual
• temporal
– auditory, memory areas
• olfactory
– smell
Brain Disorders
• Traumatic Brain Disorders
Brain Disorders
• Degenerative Brain Diseases
– cerebrovascular accident “stroke”
• 3rd cause of death in US
– ischemia: lack of oxygen
– transient ischemia attacks
– Alzheimer’s disease
• plaque & tangles in the brain
– Sclerosis
• myelin is destroyed
– Cerebral palsy
• temporary lack of oxygen
• brain damage, lack of muscle control, paralysis
The Spinal Cord
• 31 prs of spinal nerves
• structure
– gray matter
– white matter
– disorders and imbalances
• paralysis
– paraplegia - only legs
– quadriplegia - all limbs
• spinal shocks
– transient functional loss
• Cranial Nerves ~ 12 prs (head & neck)
– Nerves
I olfactory: smell
II optic: vision
III oculomotor: pupil size, move eyes
IV trochlear: eye movement
V trigeminal: chewing, pain, temp., touch
VI abducens: rolls eyeballs
VII Facial- facial expression
VIII vestibulocochlear: hearing, balance
IX glossopharyngeal: saliva, lacrimal,
swallow
• X vagus: digestive, peristalsis, heart slows
• XI accessory: neck & back muscles
• XII hypoglossal: tongue
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Peripheral Nervous System
• The Spinal Nerves
– Plexuses
• network of nerves
– Cervical
– Brachial
• axillary
– Lumbar
• femoral
– Sacral
• sciatic
Autonomic Nervous System
• Sympathetic
– thoracolumbar
– flight or fright
• norepinephrine
• Parasympathetic
– craniasacral
– rest and digest
– vagus nerve
• acetylcholine
Effects on Organs/ systems
Organs
Sympathetic
Parasympathetic
Heart
Speeds up
Slows down
Arteries
Constricted
b.p. up
Decreased
peristalsis
Constricts
sphincters
Dilate
Dilate increased to
dig organs
Increased
peristalsis
Relax sphincters
Dilate
Constrict
Decreases
Increases
Digestive
organs
Urinary
bladder
Bronchi
trachae
Iris pupil
Saliva
Constrict