Chapter 2: Basic Brain Anatomy

Central Nervous System (CNS)

• Brain & spinal cord
• Entirely encased by bone

Peripheral Nervous System (PNS)

• Nerve tracts that connect the rest of the body to the CNS

The brain has 3 divisions:

Cerebrum
Brain stem
Cerebellum

Cerebrum

• Houses the highest & most complex cognitive functions
• Is folded in on itself so that more neural tissue
can be packed into a much smaller space
• Ridges = gyri/gyrus (singular)
• Valleys = sulci/sulcus (singular)
• Cerebrum rests on top of the brainstem

Gray Matter

• Unmyelinated neurons responsible for processing & regulating information within the nervous system
• Found in the cortex, some subcortical structures, and spinal cord

White Matter

• Myelinated neurons specializing in transmitting information over relatively long distances within the body
• From one area of the brain to another or between the brain & the body

Association Fibers

White matter pathways that connect different structures & areas of the brain within a single hemisphere

Commissural Fibers

White matter pathways that connect analogous areas between the two cerebral hemispheres

Projection Fibers

• White matter pathways that project from the brain to the spinal cord
• Transmit motor signals from the CNS to the PNS
• Transmit sensory signals from the PNS back up through the lower CNS to be processed in the brain

Cerebral Meninges

• Between the surface of the brain & the skull are 3 anatomic layers of tissues
• Various functions
• Encase the brain & spinal cord

Dura Mater

• “Tough mother”
• Dense, fibrous protective layer of tissue enveloping the brain & spinal cord
• Most superficial layer of the cerebral meninges

Arachnoid Mater

• Spider web-like appearance of blood vessels
• More delicate than the dura mater
• Wraps the brain & spinal cord
• Supplyies blood to the surface of the brain through the many blood vessels it contains

Pia Mater

• “Gentle mother”
• Innermost & delicate layer
• Closely hugs the surface of the brain & spinal cord
• Rises & falls along the gyri, sulci, & fissures of the brain

Ventricular System

• Between the arachnoid mater and the pia mater as well as within the ventricles (cavities) in the brain
• Houses a nutritive & colorless fluid known as cerebrospinal fluid
• Has 4 ventricles

2 Lateral Ventricles

• Large cerebrospinal fluid-filled cavities on which the cerebrum rests
• Most of the cerebrospinal fluid within the cerebrospinal fluid system is produced by tissues within the lateral ventricles known as the choroid plexus

Foramen of Monro

• Connects the lateral ventricles to the 3rd
ventricle

Aqueduct of Sylvius

• Connects the 3rd ventricle to the 4th ventricle that is associated with the brain stem

Functions of the Ventricular System

• The ventricular system helps cushion the brain from trauma
• Manufactures & circulates cerebrospinal fluid to deliver nutrients to the brain & remove waste

Fissures

• Deeper grooves that make pronounced divisions in the anatomy of the brain

Longitudinal Fissure

• A deep groove running front to back
• Divides the brain into left & right halves (left & right cerebral hemispheres)
• Each hemisphere is responsible for different cognitive & motor functions

Corpus Collosum

• The 2 hemispheres work in tandem and communicate with
one another by a mass of white matter tracts
• Found deep within the longitudinal fissure

The left hemisphere

language-dominant hemisphere

The right hemisphere

nondominated hemisphere for language

The right hemisphere specializes

in the nonlinguistic aspects of communication (facial expressions, body language, gestures, prosody)

Prosody

is the changes in tone and intensity we use when we speak that allow us to give the words we say an emotional component

Individuals with right hemisphere damage tend

to be very literal and concrete in their comprehension of language

Right hemisphere responsibilities:

processing & recognizing faces and facial expressions

Prosopagnosia

is a neurological deficit in the specific ability to cognitively process sensory information regarding the faces of others for the purpose of recognition

Amusia

is the loss of the ability to recognize and interpret music

Macrostructure

the bigger picture composed of many details. Also known as the gestalt

Gestalt

an organized whole that is perceived as more than the sum of its parts

Macrostructure Processing

the ability to effectively piece together many smaller details to arrive at the correct perception of the big picture (the macrostructure)

Right Hemisphere:

• The spatial component of math skills
• Visuospatial processing

Visuospatial Skills:

perceiving depth, distance, shape, localizing targets in space

The right hemisphere also plays a role in the ability to attend

to stimuli (sustained, selective attention)

Broca’s Area

• The inferior, posterior region of the frontal lobe of the left hemisphere
• A specialized area of the cerebrum responsible for finding and assembling words for the expression of thought
• Damage to this area can produce Broca’s Aphasia

Wernicke’s Area

• A specialized position of the cerebrum located at the superior
marginal gyrus of the left hemisphere’s temporal lobe
• Responsible for interpreting and deriving meaning from the speech of others
• Damage to this area can produce Wernicke’s Aphasia

Central Sulcus (Fissure of Rolando)

A deep groove that runs down the middle lateral surface of each cerebral hemisphere

Lateral Sulcus (Sylvian Fissure)

A deep groove that begins at the lower frontal aspect of each of the 2 cerebral hemispheres and travels at an upward
angle, passes the central sulcus and then terminates

Frontal Lobes

• Anterior sections of the cerebral hemispheres that are delineated posteriorly by the central sulcus and inferiorly by the lateral sulcus
• Houses expressive language within the left and deals heavily in motor movement bilaterally

All voluntary movement originates in the

frontal lobes

Primary Motor Cortex

A strip of tissue oriented vertically along the last gyrus of each frontal lobe that plays a large role in voluntary motor movement

Motor Homunculus

A visual illustration of the amount of cortical tissue dedicated to the movement of each body part within the primary motor cortex

The left primary motor cortex is

responsible for issuing motor movement for speech

Damage at or near Broca’s area, near the base of the left primary motor cortex, disrupts

the brain ability to execute appropriate motor plans for speech
(apraxia)

The frontal lobes (especially the prefrontal lobes) store

personality and some memory

The Primary Sensory Cortex (Sensory Strip)

A section of the cortex along the first gyrus of the parietal lobe
dedicated to receiving and processing sensory information

Sensory Homunculus

A visual illustration of the amount of cortical tissue within the primary sensory cortex dedicated to processing sensory information from each body part

Proprioception

An individual’s sense of where his or her extremities and body are in space

Temporal Lobes

Located inferiorly to the posterior portion of the frontal lobes and inferiorly to the anterior portions of the parietal lobes

The Hippocampus

• House more memory than any other cerebral lobes
• Most of the memory ability of the temporal lobes can be attributed to the hippocampus Hippocampus is Latin for
“seahorse”

Temporal Lobes: Memory

Located within the inferior and medial section of the temporal lobes where the cortex curls up into itself

The hippocampal region takes new experiences and
turns them

into memories that can be stored and accessed later

Damage to the hippocampal regions in both temporal lobes cause

severe-profound deficits in short term memory

Primary Auditory Cortex

• Located on the superior temporal gyrus, anterior to Wernicke’s area in the left hemisphere
• The section of the temporal lobes that first receives neural impulses of sound from the ears

Occipital Lobes

• The most posterior of the cerebral lobes
• Behind the parietal & temporal lobes
• Concerned mostly with vision
• House the primary visual cortex which receives visual information from the eyes

Visual Association Cortex

• Anterior to the primary visual cortex
• Processes & interprets visual information received from the
primary visual cortex
• Allows for visual perception
• Allows people to “make sense” with their brain what they are
seeing with their eyes

Visual Agnosia

• Bilateral lesions in the visual association cortices
• Person can see but cannot comprehend what they are seeing

The subcortex

• Is responsible for performing functions that are automatic & are beneath the level of awareness
• Deals with life-sustaining functions such as regulating heartbeat & level of arousal

• Includes:
• The brain stem
• Cerebellum
• Thalamus
• Basal ganglia
• Limbic system

The Brain Stem

• A subcortical structure
• Connects the spinal cord to the brain
• Houses many structures involved in autonomic functions

Midbrain

superior most section of the brain stem; houses the substantianigra (produces the neurotransmitter, dopamine)

Pons

provides an attachment between the cerebellum and the rest of the CNS, bulbous in shape

Medulla

many of the motor neuron fibers that transmit impulses of motor movement cross over to the other side of the brain

reticular formation

Stretching between the midbrain, pons, and medulla is a series of nuclei

Cerebellum

Hangs off the back of the brain stem under the occipital lobes
• “little brain”
• Known as an error control device for body movements; ensures that body movements are smoothly coordinated and as error free as possible (alters force, timing & sequencing of muscle contractions)

ataxia dysarthria

Pathology of the cerebellum often produces a speech problem

The Thalamus

• Sits on top of the brain stem and under the cerebral hemispheres
• The thalamus is responsible for taking sensory signals from one part of the nervous system and directing them to another part of the nervous system

• Functions as the “relay station” for neural impulses of sensation

The Basal Ganglia

• A group of subcortical structures located deep within the cerebral hemisphere on either side of the thalamus
• Works to regulate body movement
• Includes the caudate nucleus, the putamen, and the globus pallidus

• Lesions to the basal ganglia create problems with initiation of
movement, muscle tone, and involuntary movements

The Limbic System

• A number of subcortical structures responsible for sense of pleasure, flight- or-flight response, emotions, emotional memory and sense of motivation
• Disturbances of the limbic system can create difficulties such as emotional imbalances, anxiety disorders, panic
attacks

Spinal Cord

• A bundle of white matter tracts and gray matter housed within the bony vertebral column
• Afferent (sensory) impulses coming from the body to be transmitted to the brain
• Efferent (motor) impulses from the brain to be transmitted to the body
• Originates superiorly at the medulla

reflex

the production of a physical movement that occurs automatically in response to a stimulus and is initiated
below the level of awareness

stretch reflex

• A contraction of a muscle in response to a passive stretching of a muscle spindle within a muscle
• Enables the body to correct any unintended changes in body position in a timely manner without waiting for input
from the cerebral cortex
• Keeps appropriate tone in the muscle

Spasticity

a combination of hypertonia & resistance to passive movement caused by a hyperactive stretch reflex that makes movement of a body part difficult

Blood Supply to the Brain

• Brain consumes 20-25% of the total amount of oxygen & glucose used by the body
• To keep the supply of blood to the brain necessary to meet these massive requirements, the body must get blood first
from the heart to the head

Internal Carotid Arteries & Vertebral
Arteries

• 2 pairs of large arteries
• Function: to deliver blood superiorly to the brain to be distributed throughout the brain by other arteries

Internal Carotid Arteries

• Paired right and left internal carotid arteries course superiorly from the thorax in the anterior portion of the neck
• The pulse in the neck is felt by palpating the internal carotid
• Course through the neck to the base of the brain to link with the Circle of Willis
• Once the internal carotid arteries reach the Circle of Willis, the paired left and right anterior cerebral arteries and the middle cerebral arteries branch off from the internal carotids

Anterior Cerebral Arteries

• Course anteriorly to supply blood to: Frontal lobes
• Course superiorly to supply blood to: Parietal lobes, Basal ganglia, and Corpus callosum

Middle Cerebral Arteries

Course laterally to supply blood to:
• Broca’s area
• Wernicke’s area
• Temporal lobes
• Primary motor cortex

Vertebral Arteries

• Paired right and left
• Course superiorly through the cervical vertebrae of the spinal column in the posterior aspect of the neck
• Come together to form the basilar artery at the pons

Circle of Willis

• A series of connections between arteries that connect the internal carotid and vertebral/basilar system
• Ensures equal blood flow to all areas of the brain
• Acts as a safety valve if an occlusion occurs within it or below it
• Forms a circle at the base of the brain

anterior communicating artery

connects the left and right anterior cerebral arteries

posterior communicating artery

links the posterior cerebral arteries to the middle cerebral arteries

Afferent signals

originates with the body are transmitted along the PNS on
their way back to the CNS for processing

Efferent signals

from the brain travel along the PNS to reach the muscles to
command them to move

Spinal Nerves

• Course between the spinal cord and the body
• Contribute to control of the trunk, arms, legs
• 31 pairs of spinal nerves
• Arises within the gray matter of the spinal cord
• Courses out from between the bones of the vertebral column