BSCI450: Central Nervous System (CNS)

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and spinal cord

Two major divisions of the CNS (central nervous system)

Brain and spinal cord

Average adult brain weight

Approximately 3.5 lb (1.4–1.6 kg).

Brain size and intelligence

Brain size alone does not determine intelligence

What factors are more closely related to intelligence?

Degree of cortical folding, increased cortical surface area, and number of synaptic connections

Cortical folding

The folding pattern of the cerebral cortex that increases surface area and allows more neurons and synapses

Gyri

Raised folds of the cerebral cortex

Sulci

Shallow grooves between gyri

Fissures

Deep grooves that separate major brain regions

Microcephaly

A condition involving an abnormally small brain size that may be associated with reduced intelligence

Four major regions of the brain

1. Cerebrum

2. Diencephalon

3. Brainstem

4. Cerebellum

Cerebrum

The largest brain region, making up approximately 80–83% of total brain mass

Diencephalon

A brain region containing the thalamus, hypothalamus, and epithalamus

Brainstem

A region containing the midbrain, pons, and medulla oblongata

Cerebellum

A brain region responsible for coordination of movement, posture, and balance; makes up about 11% of brain mass

Coordinates movement but does not initiate movement

How does the cerebellum contribute to alcohol intoxication?

throws the body off balance since it processes information from cerebral motor areas, visual and equilibrium inputs → smooth and coordinated skilled voluntary skeletal muscle movements, equilibrium/maintenance of balance

Four structures protecting the brain

1. Cranium

2. Meninges

3. Cerebrospinal fluid (CSF)

4. Blood-brain barrier

Cranium

The skull structure that protects the brain

Cranial vault (neurocranium)

The collection of cranial bones that surrounds and protects the brain

Eight cranial bones

* Frontal

* Occipital

* Two parietal

* Two temporal

* Sphenoid

* Ethmoid

Meninges

Three connective tissue membranes surrounding and protecting the brain and spinal cord

Three layers of meninges

1. Dura mater

2. Arachnoid mater

3. Pia mater

Dura mater

The outermost, toughest meningeal layer that lines the skull and anchors the brain

Arachnoid mater

The middle meningeal layer containing the subarachnoid space (contains cerebralspinal fluid or CSF)

Subarachnoid space

The space between the arachnoid mater and pia mater that contains cerebrospinal fluid

Pia mater

The innermost, thin meningeal layer that closely adheres to the brain surface and directly contacts neurons

Cerebrospinal Fluid (CSF)

A fluid surrounding the brain and spinal cord that provides protection, nutrients, and waste removal

Functions of CSF

* Cushions the brain

* Provides buoyancy

* Delivers oxygen

* Delivers nutrients

* Removes carbon dioxide

* Removes metabolic waste

Why CSF is important?

Neurons require protection because the blood-brain barrier limits substances entering the nervous system

Blood-brain barrier is a selective barrier that prevents harmful substance in blood from crossing to the brain to affect their functions (revolves around astrocytes in the brain)

Hydrocephalus

Excess accumulation of cerebrospinal fluid

Causes of hydrocephalus

* Excess CSF production

* Poor CSF drainage

Cerebrum

The largest brain region responsible for higher functions such as movement, thought, sensation, and language → 80-83% of the brain

Percentage of brain mass made up by cerebrum

Approximately 80–83%

Longitudinal fissure

The deep groove separating the right and left cerebral hemispheres

Contralateral control

The concept that one side of the brain controls the opposite side of the body

Five lobes of each cerebral hemisphere

1. Frontal

2. Parietal

3. Temporal

4. Occipital

5. Insula

Frontal lobe

* Voluntary movement

* Thinking

* Planning

* Organization

* Personality

* Motor speech

Broca’s area

A motor speech area located in the left frontal lobe responsible for producing speech

Parietal lobe

Processes somatic sensation

integrates information about spatial relationships, perception and sensory input from the body (e.g. Touch, Pressure, Pain, Temperature, Body position)

Temporal lobe

* Hearing

* Memory

* Language comprehension

• hippocampus in this lobe → long-term memory

Hippocampus

in temporal lobe

involves with long-term memory

Wernicke’s area

A language comprehension area located in the left temporal lobe

Occipital lobe

Visual processing

controls ability to see and combine colors, shapes, angles, and movement into meaningful patterns

Insula

Deep to the lateral sulcus

Contains the primary gustatory cortex responsible for taste

Gray matter

Neural tissue containing neuron cell bodies, dendrites, and unmyelinated axons

white matter

Neural tissue containing myelinated axons

Forms communication pathways called tracts

What does the left side of the brain control?

• speech organization

• logic

• analysis

• sequencing

• linear

• mathematics

• facts

• think in words

• words of songs

• computation

What does the right side of the brain control?

• creativity

• imagination

• holistic thinking

• intuition

• art (motor skill)

• rhythm (beats)

• non-verbal

• feelings

• visualization

• tune of songs

• daydreaming

Basal nuclei

Clusters of neuron cell bodies located deep within cerebral white matter

* Initiate movement

* Stop movement

Parkinson disease

A neurological disorder caused by loss of dopamine input to the basal nuclei.

Cause of Parkinson disease

Degeneration of dopaminergic neurons in the substantia nigra.

Parkinson disease symptoms

* Difficulty initiating movement

* Difficulty stopping movement

* Resting tremor

Three functional categories of cerebral cortex

1. Motor areas

2. Sensory areas

3. Association areas

Motor areas

Entirely within the frontal lobe.

Primary motor cortex

The region responsible for voluntary skeletal muscle movement, present in both cerebral hemispheres for contralateral voluntary control for movement → precentral gyrus

Premotor cortex

present in both cerebral hemispheres and involved in controlling skeletal muscles used in activities repetitive in nature

Broca’s area

Frontal eye field

present in both hemispheres to control extrinsic eye muscles that position the eyes

Pyramidal cells

Neurons in the primary motor cortex whose axons form corticospinal tracts → pathways carry signals from brain to skeletal muscles

The left motor cortex controls the right side of the body, and the right motor cortex controls the left side during the crossing of corticospinal tracts in the medulla oblongata

Sensory areas

for conscious awareness of sensation

consists of:

• primary somatosensory cortex in parietal lobes

• primary visual cortex in occipital lobes

• primary auditory cortex in temporal

• primary olfactory cortex in temporal and frontal

• primary gustatory cortex in insula

what causes a left brain stroke?

Causes right-sided paralysis

what causes a right brain stroke?

Causes left-sided paralysis

Hemiplegia

Paralysis of one side of the body (ex: damage to the RIGHT precentral gyrus results in paralysis on the LEFT side of the body; damage to the LEFT precentral gyrus results in paralysis on the RIGHT side of the body)

Broca aphasia

A language disorder where a person understands language but cannot produce fluent speech.

Broca aphasia characteristics

* Short speech

* Broken speech

* Single words

Wernicke aphasia

A disorder where speech is fluent but meaningless → disruption in language sequencing/comprehension

Conduction aphasia

A language disorder caused by damage to the arcuate fasciculus.

Conduction aphasia symptoms

* Can understand speech

* Can produce speech

* Cannot repeat phrases

Premotor cortex

Controls learned repetitive movements.

Examples controlled by premotor cortex

* Typing

* Playing piano

* Instrument performance

Frontal eye field (FEF)

A frontal lobe region controlling voluntary eye movements.

Frontal eye field function

Controls extraocular muscles.

Frontal eye field lesion effect

Eyes deviate toward the side of the lesion.

what happens to the damage to the left frontal eye field?

results in both eyes deviated to the left (left gaze), RIGHT SIDE body damage

what happens to the damage to the right frontal eye field?

results in both eyes deviated to the right (right gaze), LEFT SIDE body damage

White matter tracts

Bundles of myelinated axons that allow communication between different areas of the nervous system

Three types of white matter tracts

1. Commissural tracts

2. Association tracts

3. Projection tracts

Commissural tracts

White matter pathways connecting the left and right cerebral hemispheres

Association tracts

White matter pathways connecting regions within the same cerebral hemisphere

Projection tracts

White matter pathways connecting the brain with the spinal cord

Diencephalon

A brain region containing the thalamus, hypothalamus, and epithalamus

Thalamus

A sensory relay center that directs information to the cerebral cortex (not processed one way).

Approximately 80%.

Gateway to the cerebral cortex.

Relays almost all sensory information to the cortex except smell.

Hypothalamus

A major autonomic control center responsible for maintaining homeostasis, located below thalamus.

Hypothalamus functions

* Body temperature regulation

* Hunger control

* Satiety

* Water intake

* Emotional responses

* Circadian rhythm

* Sleep-wake cycle

* Endocrine regulation → produces 9 hormones

* Homeostasis

Epithalamus

A region of the diencephalon containing the pineal gland → endocrine gland secreting hormone, melatonin.

forms roof of third ventricle

Pineal gland

A gland that releases melatonin → sleep inducing chemical that regulates sleep patterns

Brainstem

A region of the brain responsible for communication pathways and vital autonomic functions

Three regions of the brainstem

1. Midbrain

2. Pons

3. Medulla oblongata

Midbrain

The superior region of the brainstem involved in movement control and sensory processing.

Substantia nigra

A midbrain structure that produces dopamine.

Function of substantia nigra dopamine

Provides dopamine input to the basal nuclei.

Substantia nigra degeneration

Causes Parkinson disease.

Function of substantia nigra dopamine

Provides dopamine input to the basal nuclei.

substantia nigra degeneration causes Parkinson disease.

Pons

The middle region of the brainstem involved in breathing regulation.

Respiratory centers in the pons

* Pneumotaxic center

* Apneustic center

Function of pontine respiratory centers

Help regulate breathing patterns.

Medulla oblongata

The inferior portion of the brainstem responsible for vital autonomic functions.

* Heart rate

* Blood pressure

* Breathing

* Swallowing

* Vomiting

* Cough reflex

Cerebellum function

Coordinates movement, posture, and balance, visual and equilibrium inputs, smooth and coordinated skilled voluntary skeletal muscle movements.

11% of total brain mass → “little brain”

in cross section → outer gray cortex - inner white matter with pattern that resembles branching tree and referred to as the Arbor Vitae

Cerebellum does not

Initiate movement.

Spinal cord

The second major component of the central nervous system that connects the brain to the peripheral nervous system.

Location of the spinal cord

Begins where the medulla oblongata ends and extends to approximately the L1 vertebra (sometimes L2).

Average adult spinal cord length

Approximately 42 cm (17 inches).

Primary functions of the spinal cord

* Carries sensory information to the brain.

* Carries motor commands from the brain.

* Serves as a reflex center.

Ascending tracts

White matter pathways that carry sensory information to the brain

Descending tracts

White matter pathways that carry motor commands from the brain to the body

Arrangement of white and gray matter in the spinal cord

White matter is on the outside (myelinated axons), and gray matter is on the inside (unmyelinated axons)

Dorsal horn

The posterior gray matter region that receives sensory (afferent) information.

Receives sensory signals and sends them toward the brain.

Dorsal equals what? Sensory or motor?

Sensory (afferent)

Ventral horn

The anterior gray matter region containing motor neuron cell bodies.

Sends motor (efferent) signals to skeletal muscles.

Ventral equals what? Sensory or motor?

Motor (efferent)

Structures protecting the spinal cord

* Vertebral column

* Meninges

* Cerebrospinal fluid (CSF)

Vertebral column

Provides mechanical protection for the spinal cord.

Intervertebral discs → Fibrocartilage pads between vertebrae that absorb shock and allow movement.

Spinal meninges

* Dura mater

* Arachnoid mater

* Pia mater

Epidural space

The space between the spinal dura mater and vertebral bones.

Contents of the epidural space

* Fat

* Veins

* Pain fibers

Central canal

A narrow channel running through the center of the spinal cord that contains CSF.

Equivalent structure in the brain

The ventricles.

Spina bifida

A congenital defect in which the vertebral arches fail to close completely.

Structures affected in spina bifida

* Spinal cord

* Spinal nerves

Two spinal enlargements

• Cervical enlargement → The widened region of the spinal cord supplying skeletal muscles above the diaphragm and the upper limbs.

• lumbar enlargement → The widened region supplying skeletal muscles below the diaphragm and the lower limbs.

Cervical enlargement

The widened region of the spinal cord supplying skeletal muscles above the diaphragm and the upper limbs.

lumbar enlargement

The widened region supplying skeletal muscles below the diaphragm and the lower limbs.