THE FUNCTIONS OF
THE NERVOUS
SYSTEM
The Central Nervous System
THE CENTRAL
NERVOUS SYSTEM
• The nervous system is divided into two subunits
• Central nervous system (CNS)
– Brain
– spinal cord.
• Peripheral nervous system
– Any part of nervous system outside of CNS
– Afferent and efferent.
THE Cells of the CENTRAL
NERVOUS SYSTEM
• Contains neurons: obviously single neural cells.
• Nucleus
– A group of cell bodies (somas) in the CNS and a
• Ganglion
– Group of cell bodies in the peripheral nervous system.
THE Cells of the CENTRAL
NERVOUS SYSTEM
• Contains neurons: obviously single neural cells.
• Nerve :
– is a bundle of axons running together
– like a multi-wire cable.
– Nerve is used only in the peripheral nervous system.
• Tracts.
– Bundles of neurons
– Inside the CNS
– Tracts = nerves
Divisions of the CNS
• Forebrain
– Cerebral hemispheres
• Frontal lobe
• Parietal lobe
• Occipital lobe
• Temporal lobe
– Thalamus and hypothalamus
– Corpus callosum
– Ventricles
• Midbrain and Hindbrain
–
–
–
–
Superior colliculi
Thalamus
Pineal gland
Hindbrain
• Pons;
• Medulla;
• Reticular activating system
• Spinal Cord
Let’s start at the top! The Forebrain!
THE Forebrain
• Forebrain
– two cerebral hemispheres,
– the thalamus,
– the hypothalamus.
• The large, wrinkled cerebral hemispheres dominate the
brain’s appearance.
• The longitudinal fissure
– that runs the length of the brain
– separates the two cerebral hemispheres,
– Two cerebral hemispheres are mirror images of each other in appearance.
• Remember:
– Left hemisphere brain controls right side of body
– Right brain hemisphere controls left side of body
Gyri and sulci
• The brain’s surface has many ridges and grooves
that give it a very wrinkled appearance.
• Several geographic landmarks:
– gyrus. Each ridge
– a sulcus The groove or space between two
– Fissure: large sulcus
Gyrus
Sulcus
convolutions of
the cortex
• The outer surface is the cortex, which is made up
mostly of the cell bodies of neurons.
– Because cell bodies are not myelinated, the cortex looks
grayish in color,
– Thus referred to as gray matter.
• The cortex is only 1.5 – 4 mm thick,
• Convolutions (folds) increase the amount of cortex by
tripling the surface area.
– Also provides axons easier access to cell bodies
– Axons come together at central core of each gyrus
– Here the brain appears white
Organization of the
CENTRAL NERVOUS SYSTEM
• The central nervous system is arranged in a hierarchy.
• As you ascend from the spinal cord through the
hindbrain and midbrain to the forebrain, the neural
structures become more complex and so do the
behaviors they control.
• The hemispheres are divided into four lobes –
–
–
–
–
–
frontal
parietal,
occipital
temporal
each named after the bone of the skull above it.
Is size important?
• Relation of brain size to body size versus intelligence
– Brain size more related to body size
– Brains of elephants and sperm whales 5-6x larger than human brain
• What is important?
–
–
–
–
Convolutions are the important variable!
Greater number of gyri = more cortex
Also; more gyri in cerebral hemispheres than lower brain parts
More surface area = more connections
THE frontal lobe
• Frontal lobe
– anterior to (in front of) the central sulcus
– superior to (above) the lateral fissure.
• Precentral gyrus,
– extends the length of the central sulcus
– Contains primary motor cortex, which controls voluntary (nonreflexive)
movement.
– The parts of the body are “mapped onto” the motor area of each
hemisphere
– Can be illustrated in the form of a homunculus, which means “little
man.”
• The secondary motor areas are located just anterior to the
primary area.
THE motor homunculus
•More brain area is devoted to parts of
body with greater/finer motor movement
•Fingers
•Hands
•Lips
•Legs
•Arms
•Little brain area devoted to motor
movement of back, toes, etc.
broca’s area
• Broca’s area is located
anterior to the motor
area and along the
lateral fissure.
• Broca’s area controls
speech production
• contributes the
movements involved in
speech and grammatical
structure.
THE prefrontal cortex
• Prefrontal Cortex –
–
–
–
–
The most anterior part of the frontal lobes
largest region in the human brain,
Twice as large as in chimpanzees,
Accounts for 29% of the total cortex.
• The prefrontal cortex is involved in
–
–
–
–
Planning and organization,
Impulse control,
Adjusting behavior in response to rewards and punishments,
Some forms of decision making.
THE prefrontal cortex
Prefrontal
Cortex
THE prefrontal cortex
• How know the effects of the Prefrontal cortex?
– During the 1940s and 1950s surgeons performed tens of thousands of
lobotomies, a surgical procedure that disconnected the prefrontal area
from the rest of the brain.
– Initially the surgeries were performed on very disordered
schizophrenics, but many overly enthusiastic doctors lobotomized
patients with much milder problems.
• Effects?
– The surgery calmed agitated patients,
– Benefits came at a high price in that patients often became:
• emotionally blunted
• distractible
• childlike in behavior.
• Psychosurgery rarely used today to treat psychiatric problems
THE parietal lobes
• Parietal lobes
– located superior to the lateral
fissure
– between the central sulcus and
the occipital lobe.
• Primary somatosensory
cortex
– located on the postcentral gyrus,
– processes the skin senses (touch,
warmth, cold, and pain),
– Also senses that inform us about
body position and movement.
THE somatosensory
homunculus
• The somatosensory
cortex also is
organized as a
homunculus,
– size of each area
depends on the
sensitivity in that part
of the body.
THE parietal
association areas
• Association areas
– Contained in each of the lobes
– carry out further processing beyond what the primary area does
– often combine information from other senses.
• Parietal lobe association areas:
–
–
–
–
receive input from the body senses and from vision.
Help a person identify objects by touch
help determine the location of the limbs
Help locate objects in space.
• Damage to the posterior parietal cortex may produce sensory
neglect: a disorder in which the person ignores
–
–
–
–
objects,
people,
activity on the side opposite the damage.
Why the opposite side of the damage?
THE temporal lobe
• Temporal lobes
• Separated from the frontal
and parietal lobe by the lateral
fissure
• Three important areas:
– Auditory projection area,
– visual and auditory association areas
– Additional language area: Wernicke’s
Area.
THE auditory or
temporal cortex
• Auditory cortex:
– receives sound information from the ears
– lies on the superior (uppermost) gyrus of the temporal lobe.
• Wernicke’s area
– Just posterior to the auditory cortex
– interprets language input arriving from the nearby auditory and visual areas.
– also generates spoken language through Broca’s area and written
language by the way of the motor cortex.
• Inferior temporal cortex
– lower part of the lobe (as the name implies)
– plays a major role in the visual identification of objects.
THE occipital cortex
• Occipital lobes
– location of the visual cortex,
– visual information is
processed.
• contains a map of visual
space because adjacent
receptors in the back of
the eye send neurons to
adjacent cells in the visual
cortex.