Ch. 12: The Central Nervous System

What develops from the embryonic neural tube?

The central nervous system (CNS).

What does the anterior end of the neural tube become?

It becomes the brain.

What does the posterior end of the neural tube become?

It becomes the spinal cord.

What are the paired superior parts of the brain called?

The cerebral hemispheres (cerebrum).

What is the largest portion of the brain?

The cerebrum.

What is the average weight of the cerebrum in females?

1450g

What is the average weight of the cerebrum in males?

1600g

What are the elevated ridges on the surface of the cerebrum called?

Gyri

What are the shallow grooves on the surface of the cerebrum called?

Sulci

Name some important sulci on the cerebrum.

The central sulcus, precentral gyrus, and postcentral gyrus.

What divides the cerebrum into different regions?

Fissures (deep grooves) divide the cerebrum into different regions.

Name a deep groove that divides the cerebrum.

The longitudinal fissure.

Name the surface lobes of the cerebrum.

The frontal lobe, the temporal lobe, the parietal lobe, and the occipital lobe.

What is the primary (somatic) motor cortex located in?

The frontal lobe.

What cortices are located in the temporal lobe?

The olfactory and auditory cortices.

What are the functions of the parietal lobe?

It is involved in the reception and evaluation (integration) of sensory information except for smell, hearing, and vision.

What are the functions of the occipital lobe?

It is involved in vision and the integration of visual input.

What is the function of the motor cortex in the frontal lobe?

It controls precise or skilled voluntary movements of our skeletal muscles and learned motor skills.

Is the primary motor cortex contralateral or ipsilateral?

Contralateral

What can damage to the frontal lobe cause?

Damage to localized areas of the frontal lobe (such as from a stroke) can cause paralysis of the body muscles controlled by those areas, resulting in the loss of voluntary control.

What are the two main functions of the sensory cortex in the other lobes?

The sensory cortex is involved in sensory interpretation and association.

What is sensory interpretation?

Sensory interpretation integrates sensory inputs (temp., pressure, etc.) to produce an understanding of what is being felt or observed (size, texture, etc.).

What is association in the context of the sensory cortex?

Association links sensory inputs to past memories to provide meaning to what we feel or see.

What is lateralization of cortical functioning?

It refers to the division of labor between the two cerebral hemispheres, where each hemisphere has unique abilities not entirely shared by the other.

What functions is the left cerebral hemisphere typically associated with?

The left cerebral hemisphere has greater control over language, math, and logic.

What are people who tend to be right-handed sometimes referred to as?

They are referred to as being “left-brained.”

What functions is the right cerebral hemisphere typically associated with?

The right cerebral hemisphere is more involved in intuition, emotion, and artistic and musical skills.

What are people who tend to be left-handed sometimes referred to as?

They are referred to as being “right-brained.”

What is the outer layer of the cerebrum called?

The cerebral cortex (gray matter).

How thick is the cerebral cortex?

About 2-4mm thick.

What percentage of the total brain mass does the cerebral cortex account for?

40% of the total brain mass.

What is the cerebral cortex composed mostly of?

Interneuronal cell bodies.

What are some higher brain functions associated with the cerebral cortex?

Higher brain functions associated with the cerebral cortex include speech, memory, logic, emotion, interpretation of sensory input, and consciousness.

What is the cerebral medulla?

The white matter inside the gray matter of the cerebrum.

What is the function of the cerebral medulla?

It contains myelinated nerve tracts responsible for communication between cerebral areas and between the cerebral cortex and lower CNS centers.

What is the corpus callosum?

A dense band of myelinated nerve tracts that allows communication between the left and right cerebral hemispheres.

What are the basal nuclei?

Internal islands of gray matter dispersed bilaterally in the inferior cerebrum, diencephalon, and midbrain, important in controlling and modifying motor functions.

What is Parkinson’s disease?

A condition resulting from the degeneration of dopamine-releasing neurons, leading to overactive basal nuclei and symptoms like tremors at rest.

Where is the diencephalon located?

It sits on top of the brain stem and is enclosed by the cerebral hemispheres.

What are the three parts of the diencephalon?

The thalamus, hypothalamus, and epithalamus.

Describe the thalamus.

A bilateral egg-shaped nucleus forming the superolateral walls of the 3rd ventricle, which acts as a relay station for information coming into the cerebral cortex, also providing a crude recognition of sensation.

Describe the hypothalamus.

It is located under the thalamus, capping the brain stem and forming the inferolateral walls of the 3rd ventricle. It is the main visceral control center of the body, vital for homeostasis.

What are some chief homeostatic roles of the hypothalamus?

Important autonomic control center, center for emotional response (limbic system), body temperature regulation, regulation of food intake, regulation of water balance and thirst, regulation of sleep-wake cycles, and control of endocrine system functioning.

Describe the epithalamus.

It forms the roof of the 3rd ventricle and houses the pineal gland (melatonin production) and the choroid plexus (CSF formation).

Where is the brain stem located?

It is attached to the spinal cord.

What percentage of total brain mass does the brain stem constitute?

2.5% of the total brain mass.

What is the general histological structure of the brain stem?

The brain stem is histologically similar to the spinal cord (gray matter surrounded by white matter) but has nuclei of gray matter embedded in the white matter.

What is the function of the brain stem?

It provides a pathway for fiber tracts and is associated with 10 out of 12 pairs of cranial nerves, integrating many vital functions.

What are the structures of the brain stem?

The midbrain, pons, and medulla oblongata.

What is the function of the pons?

It includes nuclei involved in the control of breathing.

Describe the medulla oblongata.

The most inferior part of the brain stem, merging into the spinal cord and containing important ascending & descending nerve tracts and autonomic control centers for vital functions.

Describe the cerebellum.

Has two hemispheres with convoluted surfaces, and accounts for about 11% of the total brain mass, providing involuntary coordination of body movements, posture, and equilibrium.

What is the function of the cerebellum?

It provides involuntary coordination of body movements, resulting in smooth, coordinated movements and agility, and also plays a role in posture and equilibrium.

What structures protect the CNS?

The scalp and skin, skull and vertebral column, and meninges.

What are the meninges?

Connective tissue membranes that lie just external to the CNS organs, covering and protecting the CNS, protecting blood vessels, enclosing venous sinuses, and containing cerebrospinal fluid (CSF).

What are the three layers of the meninges (external to internal)?

The dura mater, arachnoid mater, and pia mater.

Describe the dura mater.

The outermost layer of the meninges, with two layers that can separate to form dural sinuses (periosteum and meningeal layer).

Describe the arachnoid mater.

The middle layer of the meninges, with a subarachnoid space containing cerebrospinal fluid (CSF).

Describe the pia mater.

The innermost delicate membrane that is attached directly to the CNS organs.

What is cerebrospinal fluid (CSF)?

A fluid formed by the choroid plexus in each ventricle, similar to blood but with no red blood cells and lower protein levels, supplying nutrients and providing a protective fluid cushion.

What are the functions of CSF?

Supplies nutrients and forms a protective fluid cushion that gives buoyancy to CNS structures, reducing brain weight and preventing crushing.

Where does CSF circulate?

In the subarachnoid space, ventricles, and central canal, facilitated by ependymal cells.

Name the ventricles of the brain.

Right & left lateral ventricles (with anterior, posterior & inferior horns), 3rd ventricle, and 4th ventricle.

What are dural venous sinuses?

Blood and cerebrospinal fluid (CSF) collection sites for return to the circulatory vessels exiting the skull.

What is the blood-brain barrier?

Tight junctions between endothelial blood vessel cells, restricting the passage of many substances into the CSF.

What types of substances can easily cross the blood-brain barrier?

Lipid-soluble substances such as nicotine, ethanol, and heroin.

How do water-soluble molecules cross the blood-brain barrier?

Water-soluble molecules such as amino acids and glucose move across the blood-brain barrier by mediated transport.

Where is the blood-brain barrier very permeable?

In the vomiting center in the brain stem and in the hypothalamus.

What percentage of body weight is the brain, and what percentage of O₂ consumption does it use?

The brain is only 2% by weight but uses 20% of O₂ consumption.

Why is a constant blood supply crucial for the brain?

Nerve cells cannot store glucose or energy compounds like muscle tissue, so interrupted blood flow can cause unconsciousness or irreversible brain damage.

What is meningitis?

An inflammation of the meninges, which can be caused by bacterial (a medical emergency) or viral infections.

What is hydrocephalus?

A condition characterized by an abnormal accumulation of cerebrospinal fluid (CSF) in the brain.

What are traumatic brain injuries (head trauma)?

Injuries to the brain caused by external forces. It is the leading cause of accidental death in the U.S.

Name some types of traumatic brain injuries.

Concussion, contusion, subdural hematoma, and cerebral edema.

What are cerebrovascular accidents (CVAs or strokes)?

The death of brain tissue due to blood deprivation.

What are the main causes of strokes?

Hemorrhagic (bleeding) and ischemic (blockage) causes.

What is the glutamate cascade?

A process of neuronal damage following a stroke, where excessive glutamate release leads to neural “frying.”

What is Alzheimer's Disease?

A progressive degenerative brain disease that eventually results in dementia, characterized by abnormal protein deposits and neurofibrillary tangles.

What are some symptoms of Alzheimer's Disease?

Symptoms include memory loss, irritability, confusion, and ultimately hallucinations and death.

What is the spinal cord?

A two-way conduction system of nerve pathways to & from the brain and a major reflex center.

Where does the spinal cord extend?

From the medulla oblongata at the level of the foramen magnum to the region of L1 or L2.

What is the cauda equina?

The collection of nerve roots below L2 where the spinal cord has dispersed.

Describe the internal gray matter of the spinal cord.

It is butterfly-shaped and contains dorsal (posterior) horns, ventral (anterior) horns, lateral horns, and interneurons.

Describe the exterior white matter of the spinal cord.

It contains ascending (sensory) and descending (motor) myelinated nerve tracts organized into posterior, anterior, and lateral columns or funiculi.

What fills the central canal of the spinal cord?

Cerebrospinal fluid (CSF)

How is the spinal cord protected?

It is cushioned & protected by meninges (dura mater, arachnoid mater, and pia mater).

Describe the dura mater of the spinal cord.

It is separated from the periosteum by the epidural space and has a subdural space between it and the arachnoid mater.

Describe the arachnoid mater of the spinal cord.

It has a subarachnoid space filled with cerebrospinal fluid (CSF), where spinal taps are performed below L2.

Describe the pia mater of the spinal cord.

The innermost delicate membrane attached directly to the spinal cord.

Where do spinal nerves leave the spinal cord?

Spinal nerves leave at the level of each vertebra.

What is the dorsal root of a spinal nerve?

It contains sensory neurons, and their cell bodies form the dorsal root ganglia.

What is the ventral root of a spinal nerve?

The ventral root contains motor neurons, with their cell bodies located in the ventral horn of the gray matter.

What can direct, localized damage to the spinal cord lead to?

It can lead to functional loss.

What is flaccid paralysis?

Severe damage to the ventral root or ventral horn cells, resulting in no voluntary or involuntary muscle movement and loss of muscle tone.

What is spastic paralysis?

Damage to the cerebral cortex with spinal reflexes remaining intact, resulting in jerky, uncontrolled movements.

What is paraplegia?

Paralysis of both lower limbs due to damage or transection of the spinal cord at the level of T1-L1.

What is quadriplegia?

Paralysis of all four limbs due to damage to the spinal cord in the cervical area.

What is hemiplegia usually a result of?

Hemiplegia (paralysis to one side of the body) is usually a result of brain injury.

What is affected by a transection of the spinal cord at mid-cervical or higher?

The diaphragm, which impacts breathing.

What is Amyotrophic Lateral Sclerosis (ALS)?

A neuromuscular condition involving progressive destruction of ventral horn motor neurons, leading to loss of movement, speech, swallowing, and breathing.