THE NERVOUS SYSTEM



THE NERVOUS SYSTEM

I. The Peripheral Nervous System (PNS) – the sensory and motor neurons that connect the CNS to the rest of

the body

- the axons carrying PNS information are bundled into the electrical cables we call nerves

- has two (2) components

A. Somatic Nervous System – controls the body’s skeletal muscles

B. Autonomic Nervous System – controls the glands and muscles of the internal organs

1. Sympathetic nervous system – arouses the body, mobilizing its energy in stressful situations

2. Parasympathetic nervous system – calms the body, conserving its energy

II. The Central Nervous System (CNS) – the brain and spinal cord

A. The spinal cord – an information highway connecting the PNS to the brain

- accounts for reflexes – simple, automatic, inborn responses to sensory stimuli

- knee-jerk response

- pain reflex – reflex occurs before pain registers in brain

B. The brain

1. Lower-Level Brain Structures

a. The Brainstem – the oldest part and central core of the brain, beginning where the spinal

cord swells as it enters the skull; is responsible for automatic survival

- the crossover point, where most nerves to and from each side of the

brain connect with the body’s opposite side

i. medulla – base of the brainstem; controls heartbeat and breathing

ii. reticular formation – filters incoming stimuli and relays important information to

other areas of the brain; helps control arousal (ex: cat)

b. The Thalamus – the brain’s sensory switchboard (hub), located on top of brainstem

- receives information from senses (except smell) and routes it to areas of cortex

- transmits replies from brain to the cerebellum and medulla

c. The Cerebellum – “little brain”; helps coordinate voluntary movement and balance

- if injured, difficulty walking, keeping your balance; movements would be jerky

d. The Limbic System – donut-shaped system of neural structures; associated with

emotions such as fear and aggression and drives such as those for

food and sex; also involved in memory

i. amygdala – linked to emotion, namely aggression, rage, and fear

- ex: stimulating vs. lesioning brain of rhesus monkey

ii. hypothalamus – directs eating, drinking; regulates body temperature; helps

govern the endocrine system via the pituitary gland; is linked to

emotion; contains reward centers

iii. hippocampus – helps process explicit (facts & experiences) memories for storage

2. The Cerebral Cortex – the intricate fabric of interconnected neural cells (wrinkled grey matter) that covers the cerebral hemispheres; the body’s ultimate control & information-

processing center; divided into two hemispheres, four lobes on each side

a. Structure

- a sheet of cells 1/8 of an inch thick and containing about 20 billion neurons

- glial cells – “glue cells” that guide neural connections, provide nutrients and

insulating myelin, and mop up ions and neurotransmitters

i. frontal lobes – behind forehead; responsible for abstract thought, making plans,

judgment, making plans, creativity, & emotional control; includes the

motor cortex

ii. parietal lobes – behind frontal lobes; includes the sensory cortex

iii. occipital lobes – back of the head; primarily responsible for processing visual

stimuli

iv. temporal lobes – above the ears; primarily responsible for processing auditory

stimuli

b. Functions

i. motor cortex – area at the rear of the frontal lobes that controls voluntary

movements

- stimulating specific parts in the left/right hemisphere moves specific body

part on opposite side of body

ii. sensory cortex – area at the front of the parietal lobes that registers and processes

body sensations

iii. association areas – areas of the cerebral cortex involved in higher mental

functions such as learning, remembering, thinking, and

speaking

- frontal lobe damage can alter personality, removing inhibitions

- Phineas Gage, in 1848, had a tamping iron shot through his head,

thereby drastically altering his personality – “no longer Gage”

iv. language – a lateralized function (occurs in one hemisphere)

- Broca’s area – discovered in 1865, left frontal lobe, responsible for the

production of language

- lesion results in expressive aphasia – trouble producing speech

- Wernicke’s area – discovered in 1874, left temporal lobe, responsible for

language comprehension

- lesion results in receptive aphasia – can’t understand speech of

others & babble in meaningless speech

- angular gyrus – receives visual information and recodes it in auditory form

- lesion results in an inability to read

- nerve fibers interconnect all of these areas

c. Brain Reorganization

i. plasticity – the brain’s capacity for modification, as evident in brain reorganization

following damage (especially in children) and in experiments on the

effects of experience on brain development

- our brains are most “plastic” when we are young

3. Our Divided Brains

- for more than a century, clinical evidence has shown that the brain’s two sides serve differing

functions

a. Splitting the brain - names to associate: Sperry & Gazzaniga

i. corpus callosum – the large band of neural fibers connecting the two hemispheres

of the brain and carrying messages between them; transmit

over 1 million bits of information per second

- in early 1960s, researchers hypothesized that severing the corpus callosum would

reduce the intensity and duration of major epileptic seizures; they were right

- but, this produced a condition now called split brain, in which the two hemispheres

of the brain are isolated; it’s almost like having two minds in one head

- left hemispheric: more cheerful, sociable, self-confident, extroverted

- right hemispheric: more stressed, upset, introverted, suspicious, depressed

III. The Endocrine System – the body’s “slow” chemical communication system; a set of glands that secrete

hormones into the blood stream

A. Hormones – chemical messengers, mostly manufactured by the endocrine glands, that are produced in

one tissue and affect another

B. Pituitary Gland – the most influential, or “master,” gland. Under the influence of the hypothalamus, the

pituitary regulates growth and controls other endocrine glands

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