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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