Medical Science, Chapter 42: Nervous System

nerve net (p. 883)

hydra and other cnidarians have a network of neurons with no central organ

radial nervous system

modified nerve net with some degree of selective organization of neurons into more than a diffuse network

bilateral nervous system

nervous systems in bilaterally symmetrical animals

cerebral ganglia (p. 884)

concentration of nerve cells in the head region of planarian flatworms

evolution of nervous systems:

1. increased # of nerve cells

2. concentration of nerve cells

3. specialization of function

4. increased # of interneurons and more complex synaptic contacts

5. cephalization, or formation of a head

central nervous system (p. 885)

consists of a highly developed brain that is continuous with the dorsal, tubular spinal cord

peripheral nervous system

made up of sensory receptors (tactile, auditory, visual receptors) and the nerves, which are the communication lines

spinal cord

the cylindrical structure of nervous tissue that extends from the brain down the vertebral column, transmitting signals between the brain and the body

neural tube (p. 886)

the brain and spinal cord differentiate from single tube of tissue in early embryo

brain stem

made up of medulla, pons, and midbrain; elongated portion of the brain holding up the cerebrum

fourth ventricle

medulla’s cavity - continuous with the central canal of the spinal cord and with the channel running through the midbrain

forebrain

cerebrum, first and second ventricles

midbrain

optic lobes in fish

hindbrain

cerebullum, pons, medulla; fourth ventricle

spinal cord

central canal

superior colliculi (p. 888)

centers for visual reflexes such as pupil constriction

inferior colliculi

centers for certain auditory reflexes

red nucleus

helps maintain muscle tone and posture

thalamus

relay center for motor and sensory messages

hypothalamus

forms the floor of the third ventricle; major coordinating center for regulating autonomic and somatic responses

olfactory bulbs

important in the chemical sense of smell

cerebral cortex

grey matter - makes up the outer portion of the cerebrum

neocortex

a type of cerebral cortex in certain reptiles and all mammals

convolutions

surface area of the human cerebral cortex is greatly expanded by these folds

cerebrospinal fluid (p. 889)

shock-absorbing fluid that cushions the brain and spinal cord against mechanical injury

choroid plexus

csf is produced by these special networks of capillaries

spinal cord

extends from the base of the brain to the level of the second lumbar vertebra

ascending tracts

white matter consisting of myelinated axons arranged in bundles that conduct impulses up the cord to the brain

descending tracts

convey impulses from the cerebrum to motor nerves at various levels in the cord

steps of a reflex action (p. 890)

1. reception

2. transmission

3. integration

4. transmission

5. action by effector

medulla (p. 891)

controls heartbeat, respiration, and blood pressure

pons

respiratory and sleep centers

midbrain

visual and auditory reflexes

thalamus

sensory relay center between spinal cord and cerebrum

hypothalamus

control of body temperature, appetite, fat metabolism; sleep-wake cycle; emotional and sexual responses

cerebellum

muscle coordination and refinement of movements; muscle tone, posture, equilibrium; voluntary activity, implicit memories

cerebrum

center of intellect, memory, consciousness, and language; sensation and motor functions

cerebral cortex (outer grey matter)

motor areas: movement of voluntary muscles

sensory areas: receives incoming information from eyes, ears, pressure and touch receptors, etc.

association areas: sites of intellect, memory, language, and emotion; interprets incoming sensory information

white matter

connects neurons within the same hemisphere, right and left hemispheres, and cerebrum with other parts of brain and spinal cord

occipital lobes (p. 892)

contain visual centers

temporal lobes

centers for hearing

prefrontal cortex

evaluates information, makes judgements and decisions, planning, and organizing responses

somatosensory area

receives info regarding touch, pressure, heat, cold, and pain from skin

corpus callosum (p. 893)

large band of white matter that connects right and left hemisphere

basal ganglia

paired groups of nuclei - play a role in coordinating movement

suprachiasmatic nucleus (p. 894)

biological clock located in the hypothalamus; receives info about the duration of light and dark from the retina of the eye

reticular activating system (p. 896)

neural pathway within the brain stem and thalamus; if damaged, a person can fall into coma

REM sleep stage (p. 897)

20% of total sleep time; brain waves change to desynchronized pattern; dreams; blood flow in frontal lobes is reduced, but is increased in limbus system areas that produce visual scenes and emotion; temporary paralysis

limbic system

influences emotional aspects of behavior, evaluates rewards, and is important in motivation; influences the endocrine system and the autonomic division of the nervous system

amygdala

filters incoming sensory information and interprets it in the context of emotional needs and survival

synaptic plasticity (p. 899)

the ability of synaptic connection to change in response to experience

implicit memory

unconscious memory for perceptual and motor skills

declarative memory

factual knowledge of people, places, or objects and requires conscious recall of the information

Wernicke’s area (p. 901)

located in the temporal lobe, center for language comprehension

Broca’s area

located near motor areas in the left front lobe, control ability to speak; important in language processing and speech comprehension

cranial nerves (p. 902)

12 pairs of these in mammals transmit info to the brain from sensory receptors for smell, sight, hearing, and taste

autonomic division

helps maintain homeostasis in the internal environment; regulates heart rate and constant body temperature

para vertebral sympathetic ganglion chain (p. 904)

chain of paired sympathetic ganglia, runs on each side of the spinal cord from the neck to the abdomen

alcohol consumption in youth (p. 905)

disruption of normal growth and sexual development, abnormal brain development, memory problems, higher risk for suicide, homicide, death from poisoning

alcohol effects

at first the drinker may feel stimulated, but it actually depresses the CNS; information processing, judgment, memory, sensory perception, and motor coordination all become progressively impaired; depression and drowsiness occur

abrupt alcohol withdrawls

sleep disturbances, severe anxiety, tremors, seizures, hallucinations, and psychoses

antidepressants (p. 906)

sedation, weight gain, sexual dysfunction, nausea, headache, insomnia, anxiety, liver toxicity, excessive CNS stimulation, blood pressure, hallucinations

anti-anxiety medications

drowsiness, confusion, psychological dependence, addiction, tolerance, severe CNS depression, resulting in coma and death

antipsychotic medications

muscle spasms, shuffling gait, symptoms of Parkinson’s disease

narcotic analgesics

depress respiration, construct pupils, image coordination, tolerance, psychological dependence, addiction, convulsions, death from overdose

marijuana

in large doses, sensory distortion, hallucinations, lowered sperm counts and testosterone levels

amphetamines

tolerance, physical dependence, hallucinations, increased blood pressure, psychotic episodes, death from overdose

rohypnol (p. 907)

physical and psychological dependence, withdrawl may cause seizures

phencyclidine: “angel dust”, “ozone”

psychological dependence, craving, interferes with hormones related to growth and development, may interfere with learning, causes hallucinations, delusions, disordered thinking; high doses cause drop in blood pressure and heart rate, seizures, coma, and death; chronic use causes memory loss, difficulties with speech and thinking, and depression

lysergic acid diethylamide

impaired judgement leading to irrational behavior, panic attacks, psychosis, flashbacks

methaqualone

tolerance, physical dependence, convulsions, death

caffeine

very large doses stimulate centers in the medulla (may slow the heart), toxic doses may cause convulsions

nicotine

tolerance, physical dependence, stimulates development of atherosclerosis by stimulating synthesis of lipid in arterial wall

alcohol

physical dependence, damage to pancreas and liver, brain damage, increased risk of depression