Unit 1D: The Central Nervous System

Protective Tissues

• The CNS consists of the brain and spinal cord

• The CNS is surrounded by layers of protective tissue known as the meninges.– Swelling of the meninges due to

bacterial or viral infection is known as meningitis.

CSF and the Ventricles• The brain has a series of internal chambers that make

and distribute CSF. They are known as the ventricles.

• CSF is made from blood in the ventricles and resembles blood plasma

• The CSF:– Supports weight of brain (makes it

neutrally buoyant)– Cushions it (protects from injury)– Maintains chemical balance

• If there is a blockage to the draining of the CSF, brain damage can result

Spinal cord

• Long cable of axons that connects the brain to the peripheral nervous system.

• Runs down the inside of the vertebral column • Size:

– As thick as your pinkie finger– Only 2/3 the length of the vertebral column (17-

18in)• Function

– Carries information through motor neurons from brain to muscles and glands

– Carries information through sensory neurons from sense organs to brain

– Creates some reflexes

Spinal Nerves (PNS)

• Nerves branch off of the spinal cord at each vertebral joint.

• These nerves follow blood vessels and carry sensory and motor neuron axons

• The extent of damage from injury can be determined by location of injury

Hindbrain

• The hindbrain is responsible for life-saving functions common to all vertebrates.

• Major areas:– Cerebellum

• Receives visual, auditory, vestibular and somatosensory information and coordinates it.

• Works to make muscle movement smooth and coordinated.

Hindbrain (cont)

– Pons• Involved in sleep, respiration, swallowing, bladder

control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture• Also controls switch from inhalation to exhalation• Damage to this area can lead to “locked-in syndrome”

– Aware and awake but unable to communicate!

Hindbrain (cont)– Medulla • Regulates vital functions such as breathing, heart rate,

blood pressure, etc.• It is the brain’s connection to the spinal cord.

Midbrain

• Functions:– primary processing of auditory and visual

information (before it is passed to thalamus and cortex)• In lower vertebrates, these are the only processing

areas.

– Motor functions– Species-typical behaviors– Sleep/arousal

Forebrain

• Thalamus– Major relay center of information coming into the

brain from the senses– Regulates states of sleeping and wakefulness

Forebrain• Hypothalamus – rests below the thalamus and

above the pituitary– It is the link between the

autonomic nervous system and the endocrine system

– It is responsible for maintaining homeostasis• hunger, thirst, body temp, sleep

Forebrain

• Basal Ganglia– Involved in

movement selection and initiation

– Allows muscles to relax in motion

Forebrain

• Amygdala– Responsible for fear,

aggression, emotion

• Hippocampus– Responsible for

formation of long-term memories

Forebrain

• Cerebrum:– Largest part of human brain (most evolved)– Where conscious “thinking” takes place

• Cerebral Cortex– Outer 3mm of cerebrum (surface area = 2.5ft2)– Highly convoluted (2/3 of area is in folds)– Mostly made of cell bodies of neurons (grey matter)

• The rest of the cerebrum is made of the myelinated axons of these neurons and the fat makes this area look white - “white matter”

Regions of the Cortex• In all cases:

– the “primary cortex” area for a sense receives input directly from sense organs• Damage causes loss of sense

– The “association areas” get input from primary cortex areas and process it. Also where memories tied to those senses are stored.• Damage causes loss of

understanding– With the exception of taste and smell, the cortex receives

information from the contralateral side of the body

Regions of the Cortex

• Visual Cortex and Association Area– Sight

• Auditory Cortex and Association Area– Sound

• Motor Cortex and Prefrontal Cortex (Motor Assoc. Area)– Controls movement and

planning for movement– Specific areas control

specific body parts.

Regions of the Cortex

• Somatosensory Cortex and Association Area– Strip that transects the cerebrum

is divided into areas that respond to specific body parts (touch, feel, etc.)

– The more input and processing required for a region, the more area it is given

– Tongue/mouth and thumb/hand get most

Regions of the Cortex

• The Cerebral Cortex is often divided in lobes based upon the bones on top of the areas:– Frontal lobe

• Higher thinking, morality, decision making

– Parietal Lobe• Integrates sensory info and determines

spatial sense and navigation

– Temporal Lobe• Auditory and visual processing, speech

and long-term memory

– Occipital Lobe• Vision and dreams

Regions of the CortexSome tasks are shared equally by the hemispheres, and some tasks are lateralized. Each hemisphere has a majority of responsibility for the following:

• Left:– Sequence– Analysis– Details– Talking – Understanding– Reading– Writing

• Right– Synthesis– Perceiving

shape and size– Read maps– Building objects– Creativity

The Corpus Callosum bridges the gap between the two hemispheres.