Chapter 11: The Nervous System
Responsible for integration (decision making) and control.
CNS = Central Nervous System: brain & spinal cord: integration
PNS = Peripheral Nervous System: divided into:
Afferent division: incoming, sensory.
Efferent division: outgoing, motor, divided into
Somatic: effectors are voluntary muscles, responds to external
environment.
Autonomic: effectors are involuntary muscles and glands,
responds to internal environment, divided into
parasympathetic: maintenance
sympathetic: stress
I. Neurons
(A) Structure: cell body with nucleus, axon (transmission), dendrite(s)
(reception). Some axons with myelin sheaths for faster, saltatory (leaping)
conduction. Myelin forms white matter. Other structures form gray matter.
Neurons surrounded by neuroglia = supporting cells.
(B) Communication:
-1- impulse is the action potential on the axon. Reversal of charge- inner
membrane becomes relatively positive, a disruption of the resting membrane
potential due to an influx of Na+s. An all-or-none mechanism.
-2- synapse: a junction between a neuron and another cell, usually another
neuron. Most neurons release neurotransmitter chemicals form the axon,
requires calcium. Neurotransmitters can be excitatory or inhibitory, depends on
specific receptors on recipient cells, influenced by some drugs and toxins.
II. PNS
Contains nerves: bundles of axons, often myelinated. Biggest nerves are cranial
and spinal.
(A) Somatic division: responds to external environment, creates body
movements. Responsible for spinal reflexes, e.g. knee jerk.
(B) Autonomic division: responds to body’s internal environment.
Sympathetic and sympathetic divisions primarily antagonistic, control heart rate,
respiration, blood pressure, pupil size, digestion…..
III. CNS
(A) Protection: bone, meninges (membranes), CSF (cerebral spinal fluid),
blood brain barrier.
(B) Spinal Cord: communicates with brain, provides reflexes. Gray matter
surrounded by white matter. Dorsal sensory, ventral motor (portion infected by
the polio virus).
(C) Brain:
-1- hindbrain
a. medulla- regulates breathing, swallowing, cardiovascular functions.
b. pons- breathing.
c. cerebellum- balance, equilibrium, posture.
-2- midbrain: vision and hearing interpretation.
-3- forebrain:
a. hypothalamus: autonomic regulation, e.g. body temperature,
hormones, emotions….
b. thalamus: ‘switchboard’ relays impulses, screens them.
c. limbic system: emotions.
d. cerebrum:
two hemispheres with convoluted surface (raised gyri, indented sulci) to increase
surface area. Lobes with functional areas- sensory, motor, integrative (thinking!)
-4- scattered sytems
a. RAS = Reticular Activating System- determines level of alertness.
b. EEG = electroencephalogram- indirectly monitors brainwaves.
IV. Disorders
Trauma- head vs. spinal cord. Hemiplegia (one side paralysis, usually due to
brain damage), paraplegia, quadriplegia (based on part of spinal cord
damaged);
Infections: meningitis, encephalitis;
Epilepsy: faulty communication within CNS, seizures highly variable;
Parkinson’s Disease: lack of dopamine, loss of muscle control; Alzheimer’s
Disease: neurofibrillary tangles and protein plaques, genetic link, possible prion
infection; Tumors: usually neuroglial cells, benign, serious due to location.