Download 6.3 Central Nervous System

Chapter 6 The Nervous System
6.3
Functional Anatomy of the Central Nervous System
A. The Brain (4 parts)
- 2 to 3 pounds, 100 billion neurons, 100 billion+ glial cells
1. Cerebrum (left and right cerebral hemispheres)
a. outside of the cerebrum is the Cerebral Cortex, composed of gray matter
b. inside is white matter with interspersed gray matter, basal nuclei
c. region has: raised areas (gyrus) + grooves (sulcus) = convolutions
1. no two brains are identical
2. sulci divide the cerebrum into four lobes
- frontal = primary motor cortex (motor neurons)
Broca’s area in left frontal lobe directs speech
Associate cortex (anterior) responsible for intellect
- parietal = primary somatic sensory cortex interprets sensory
impulses
- temporal = speech, hearing, vision, memory and emotion
- occipital = vision
2. Diencephalon (interbrain)
a. thalamus – relay station for communication of sensory/motor
- also regulates state of arousal, sleep, wakefulness & high alert
b. hypothalamus – autonomic nervous system: regulates, metabolism, heart
rate, blood pressure, thirst, hunger, energy level and pleasure
c. epithalamus – includes pineal gland and regulates sleep-cycle hormones
3. Brain Stem (thumb size – three areas)
a. midbrain – relay station for sensory and motor impulses; vision, hearing,
motor activity, sleep & wake cycles, alertness, temperature regulation
b. pons – located below midbrain, helps regulate breathing
c. medulla oblongata – below the pons, regulates blood pressure, heart rate,
and breathing, controls reflexes for sneezing, coughing and vomiting
d. even with severe brain injury, as long as the brain stem is intact a person
can survive if given hydration and nutrition
4. Cerebellum (located below occipital lobe)
a. has dual hemispheres, outer gray cortex, and convolutions just like
cerebrum
b. serves to coordinate body movements and balance
5. Meninges (three protective membranes that surround brain and spinal cord)
a. dura mater (hard mother) – outer, double membrane, tough, lies beneath
the skull and around the brain
b. arachnoid mater (weblike) – middle, weblike tissue, beneath this layer is
the subarchanoid space filled with cerebrospinal fluid to cushion the
brain and spinal cord
c. pia mater (gentle mother) inner most layer attaches directly to the brain
and spinal cord
6. Blood-Brain Barrier
a. capillaries surround and nourish the brain, but these are not as permeable
to many substances like normal capillaries
b. this blood brain barrier protects the brain from surges of harmful
concentrations of hormones, ions and some nutrients
- Glucose, amino acids, water
- Alcohol, nicotine, fats, respiratory gases, anesthetics
B. Spinal Cord – extends from brain stem to the lumbar region of spine
1. Major pathway for relaying sensory impulses to the brain and motor impulses
from the brain
2. Contains neural pathways for reflex arcs
3. Is protected by three layers of the meninges and cerebrospinal fluid
4. Cross section of cord reveals a butterfly pattern of gray matter (called horns)
surrounded by white matter (called by their positions – dorsal, ventral, lateral)
5. A reflex is an involuntary and nearly instantaneous movement in response to a
stimulus. A reflex does not require any thought input.
a. nerve impulses in a reflex is called a reflex arc.
b. Sensory neurons do not pass directly into the brain, but synapse in the
spinal cord, allows reflex actions to occur relatively quickly by activating
spinal motor neurons without the delay of routing signals through the
brain, although the brain will receive sensory input while the reflex
action occurs.
c. Most reflex arcs involve only three neurons.
1. The stimulus, such as a needle stick, stimulates the pain receptors
of the skin, which initiate an impulse in a sensory neuron.
2. This travels to the spinal cord where it passes, by means of a
synapse, to a connecting neuron called the relay neuron situated in
the spinal cord.
3. The relay neuron in turn makes a synapse with one or more motor
neurons that transmit the impulse to the muscles of the limb
causing them to contract and pull away from the sharp object .
d. Reflexes do not require involvement of the brain, although in some cases
the brain can prevent reflex action.
Reflex Arc
Some Human reflexes include:

Accommodation reflex — coordinated changes in the vergence, lens shape and pupil size when looking at a
distant object after a near object.

Ankle jerk reflex — jerking of the ankle when the Achilles tendon is hit with a tendon hammer while the foot is
relaxed, stimulating the S1 reflex arc.

Asymmetric tonic neck reflex (ATNR) or tonic neck reflex — in infants up to four months of age, when the
head is turned to the side, the arm on that side will straighten and the contralateral arm will bend.

Babinski reflex — in infants up to one year of age, and also in older individuals with neurological damage, a
spreading of the toes and extension of the big toe in response to stroking the side of the foot.

Biceps reflex — a jerking of the forearm when the biceps brachii tendon is struck with a tendon hammer,
stimulating the C5 and C6 reflex arcs.

Blushing — a reddening of the face caused by embarrassment, shame, or modesty.

Brachioradialis reflex — a jerking of the forearm when the brachioradialis tendon is hit with a tendon hammer
while the arm is resting, stimulating the C5 and C6 reflex arcs.

Corneal reflex — blinking of both eyes when the cornea of either eye is touched.

Cough reflex — a rapid expulsion of air from the lungs after sudden opening of the glottis, and usually following
irritation of the trachea.

Galant reflex — in infants up to four months of age, a rotation of the upper body towards one or other side of
the back when that side is stroked.

Knee jerk or patellar reflex — a kick caused by striking the patellar tendon with a tendon hammer just below
the patella, stimulating the L4 and L3 reflex arcs.

Photic sneeze reflex — a sneeze caused by sudden exposure to bright light.

Plantar reflex — in infants up to 1 year of age, a curling of the toes when something rubs the ball of the foot.

Pupillary accommodation reflex — a reduction of pupil size in response to an object coming close to the eye.

Pupillary light reflex — a reduction of pupil size in response to light.

Rooting reflex — turning of an infant's head toward anything that strokes the cheek or mouth.

Shivering — shaking of the body in response to early hypothermia in warm-blooded animals.

Sneeze or sternutation — a convulsive expulsion of air from the lungs normally triggered by irritation of the
nasal mucosa in the nose.

Suckling reflex — sucking at anything that touches the roof of an infant's mouth.

Triceps reflex — jerking of the forearm when the triceps tendon is hit with a tendon hammer, stimulating the C7
and C6 reflex arcs.

Vestibulo-ocular reflex — movement of the eyes to the right when the head is rotated to the left, and vice
versa.