Test 3 - Central Nervous System Part 1

Development of the CNS

• Begins just before 3 weeks after conception, with the formation of the neural tube via the process of neurulation

Neurulation

• The process in which the neural tubes are formed

• Ectodermal cells migrate to meet and form the neural tubes

• The progress of the migration and formation of the neural tubes can be summed up into 4 parts:

  1. The neural plate forms from surface ectoderm

  2. The neural plate invaginates, forming the neural groove, flanked by neural folds

  3. Neural folds migrate to form the neural crest, which will form much of the PNS and many other structures

  4. The neural groove becomes the neural tube, which will form CNS structures

What does CNS stand for?

Central Nervous System

What does PNS stand for?

Peripheral Nervous System

Development of the Brain

• Once the neural tube is formed, things progress quickly

• By week 4, the brain has developed into 3 distinct areas:

  • The Prosencephalon (forebrain)

  • The Mesencephalon (midbrain)

  • The Rhombencephalon (hindbrain)

• All of these structures are hollow - remain hollow in the adult brain as well

• By 5 weeks, the Prosencephalon will develop into the Telencephalon and Diencephalon - the Mesencephalon stays just the Mesencephalon - and the Rhombencephalon will develop into the Metencephalon and Myelencephalon

By 5 weeks, what does the Prosencephalon develop into?

The Telencephalon and the Diencephalon

By 5 weeks, what does the Mesencephalon develop into?

Nothing - it remains as the Mesencephalon

By 5 weeks, what does the Rhombecephalon develop into?

The Metencephalon and the Myelencephalon

In the mature brain, what structures do the different Secondary brain vesicles develop into?

• Telencephalon - Cerebral Hemispheres and the lateral ventricles

• Diencephalon - Thalamus, Hyothalamus, Epithalamus, and the 3rd Ventricle

• Mesencephalon - midbrain and the cerebral aqueduct

• Metencephalon - pons, cerebellum, and part of the 4th ventricle

• Myelencephalon - Medulla oblongata and other part of the 4th ventricle

What is another name for the cerebral aqueduct?

Aqueduct of Silvius

What are the five lobes of the telencephalon?

• Frontal Lobe

• Prietal Lobe

• Occiptal Lobe

• Temporal Lobe

• The Insula

Telencephalon

• Results from the Prosecenphalon

• Divided into 5 lobes

• Part of the brain that you see when you pick it up (the top/outside)

Frontal Lobe

• Separated from the temporal lobe by the lateral sulcus and the parietal lobe by the central sulcus

• Initiates motor impulses

• Analyzes sensory experiences

• Provides responses to a variety of stimuli including: memory, emotions, reasoning, and verbal communication

• Contains the Precentral gyrus (primary motor area), Premotor Cortex, Broca’s area, and the Frontal eye field

Sulcus (sulci)

A groove or indentation on the surface of the brain

Gyrus (Gyri)

A ridge or projection of tissue

Precentral Gyrus

• Found in the frontal lobe

• Primary Motor Area

• Located anterior of the central sulcus

• Ridge of tissue that initiates all of our voluntary movement

• Organized into the homunculus, which means “little man”, because we can map what part of the body each section controls along it

• Face and hands take a lot more of this space, since they require a lot more coordination

Premotor Cortex

• Found in the frontal lobe

• Located just anterior to the precentral gyrus

• Involved in the motor control of learned tasks, like typing, instruments, etc.

• Works with the primary motor cortex to give our movements some skills

• If damaged, it does not affect the ability to make the movements, but it does affect the efficiency of them

Broca’s Area

• Found in the frontal lobe

• Usually on the left side of the frontal lobe

• Called the motor speech area

• Important for speaking

• Damage to this area results in an inability to express oral or written language

• Can understand language, but not express it - expressive aphasia

Frontal Eye Field

• Found in the frontal lobe

• Anterior of the premotor cortex

• Helps control voluntary eye movements

Parietal Lobe

• Found posterior to the frontal lobe

• Main boundary is the central sulcus

• Contains the Postcentral Gyrus

Postcentral Gyrus

• Found in the Parietal Lobe

• Also called the Primary Somatosensory area

• Receives all sensory input from cutaneous and muscular receptors of the body

• Also have a homunculus and an association area very similar to the motor cortex

Temporal Lobe

• Located below the parietal lobe and posterior portion of the frontal lobe

• Separated from both by the lateral sulcus

• Involved in receiving sensory auditory input from the ear

• Also interprets sensory experiences and stores memories of auditory and visual experiences

• Includes the primary auditory area, Olfactory areas, and Wernicke’s area

Primary Auditory Area

Found on the superior margin of the temporal lobe

Olfactory areas

• Located in the medial aspect of the temporal lobe in an area called the uncus

• Responsible for processing information related to smell

Wernicke’s area

• Located in the temporal lobe

• Critical for our understanding of language in any form

• Disorders in this region result in receptive aphasia

• Severe damage to this area can produce total incomprehension of either spoken or written words

Occipital Lobe

• Forms the posterior portion of the cranium and has no distinct separations

• Separated from the cerebellum by an infolding of the meningeal layer called the tentorium cerebelli

• Primarily handles vision

• Integrates eye movement by directing and focusing the eye

• Also responsible for visual association and correlating images

• Allows us to understand what a visual item represents, i.e. you know a picture of your dog isn’t really your dog, but you recognize it as your dog

• Images from the retina can be mapped in this area similar to the homunculus

The Insula

• A deep lobe that is not seen from the outside of the brain

• Deeper than the lateral sulcus and is covered by the parietal, temporal, and frontal lobes

• Integrates with other areas and may be important for memory

Prefrontal Cortex

• Functional region

• Found in the anterior portions of the frontal lobes

• Most important and complicated functional region

• Responsible for intellect, learning, cognition, and personality among other things

• Develops slowly

• Associated with mood - tumors here can cause mood swings, loss of inhibitions, and other changes in personality and behavior

• Prefrontal lobotomies used to be use to control behavior, but were found to also result in epilepsy and personality changes

Gnostic Area

• Nebulous area covering temporal, parietal, and occipital lobes

• Critical for understanding all sensory input and integrating it into a thought

• This thought is then sent to the prefrontal cortex for proper emotional interpretation and response

• Damage to this area results in an imbecile, someone who cannot interpret a situation and respond to it

Language areas

• Occur in both hemispheres of the brain, but seemed to be more concentrated in the left half

• Broca’s area

• Wernicke’s area

Expressive Aphasia

• The inability to express language, despite understanding it

• Cause by damage to Broca’s area

• i.e. you can ask them to say “pencil” and they can’t, but if you ask them to pick a pencil out of a box of pens, they can do it

Broca’s Aphasia

• Characterized by slow, labored language output of less than 10 words per minute

• Cause by damage to Broca’s area

Receptive Aphasia

• When a patient cannot comprehend spoken words, as a result of disorder in Wernicke’s area

• Have fluent, melodic speech

• However, there are numerous pauses to search for the right words, and often inappropriate words and descriptions are used

White Matter

• Found deep to the outer layer of gray matter (cerebral cortex)

• Primarily myelinated axons bundled into tracts

• These tracts can be doing 3 things, and so can be classified as:

  1. Commisural fibers

  2. Association fibers

  3. Projection fibers

Commisural fibers

Tracts of white matter that transmit information from 1 hemisphere to the other i.e. Corpus Callosum and Anterior Commissure

Association Fibers

Tracts of white matter that transmit information from 1 AREA of a hemisphere to another - a large number of these are found connecting Werncike’s area with Broca’s area

Projection Fibers

• Tracts of white matter that run vertically and are the connection of the cerebral cortex to the rest of the spinal cord and body

• consist of ascending and descending pathways

Basal Ganglia (Basal Nuclei)

• Paired masses of gray matter located deep to the white matter of the cerebrum

• 5 Masses of nuclei are considered to form the basal ganglia

• These 5 masses of nuclei are:

  • The Caudate nucleus

  • The Putamen

  • The Globus Pallidus

  • The Amygdaloid

  • The Calsutrum

Caudate Nucleus

• Part of the basal ganglia

• Seems to be involved in programmed movements

• Experiments done in cats showed that rapid stimulation of the Caudate Nucleus causes a turning of the head and circling of the animal away from the stimulus

• Low frequency stimulation causes cessation of motor activity and sleep

• Bilateral removal of both caudate nuclei causes the phenomenon of forced progression, where the animal has an irresistible tendency to move straight ahead

• In humans, loss of a portion of the caudate nucleus is also detected in Huntington’s patients

• May also be involved in the control of unconscious muscle contraction

Putamen

• Part of the basal ganglia

• In combination with the Globus Pallidus, forms the lentiform nucleus

• Appears to function similarly to the caudate nucleus

• Lesions to this have similar results to those of the caudate nucleus

Globus Pallidus

• Part of the basal ganglia

• In combination with the putamen, forms the lentiform nucleus

• Involved in motor function (programmed movements)

• Stimulation to the Globus Pallidus produces running movements and prolonged movements result in tremors on the contralateral (opposite) side

• Removal of 1 side of the globus pallidus seems to have no effect, but removal of both sides results in the animal becoming hypoactive and seldomly even changing positions

• Parkinson’s disease has been treated by surgical removal of the globus pallidus in humans

Amygdaloid Nucleus

• Part of the Basal Ganglia

• Has a function that is not totally clear

• May act more as part of the limbic system, and help put emotions into physical responses

Claustrum

• Part of the Basal Ganglia

• Function is not totally clear

Diencephalon

• The other mature structure (alongside the telencephalon) that results from the prosecenphalon

• Surrounded by the cerebral hemispheres and encloses the 3rd ventricle

• Composed of 3 parts:

  • The Thalamus

  • The Hypothalamus

  • The Epithalamus

Thalamus

• Part of the Diencephalon

• Large mass of gray matter and constitutes 80% of the diencephalon

• Main function is to act as a relay center for all sensory input (except for olfactory) before these impulses go to the cortex (postcentral gyrus)

• Divided up into 6 separate nuclei pairs, which are all specialized to respond to specific stimuli

• All sensory input has to go through the thalamus before the cortex receives it

• May also interpret and filter some information

• RELAY CENTER for the brain

Hypothalamus

• Part of the Diencephalon

• Located just below the thalamus

• form the floor and part of the walls of the 3rd ventricle

• Serves as the center for control of most autonomic functions (blood pressure, body temp, salt and water balance, etc.)

• Important for regulating the release of hormones form the anterior pituitary gland

Epithalamus

• Part of the Diencephalon

• Secretes the hormone melatonin, which is useful for sleep

• Contains the Choroids Plexus (ependymal cells secreting cerebrospinal fluid)

The Hypothalamus as a cardiovascular regulator:

• The posterior portion of the hypothalamus can produce an increase in heart rate and blood pressure, anterior portion decreases these parameters

• Sends impulses to the cardiac centers in the medulla oblongata to effect these changes

The Hypothalamus as a body temperature regulator:

• Anterior portion has temperature sensors which check body temperature

• If temp is too high, sweating, vasodilation will occur

• if temp is too low, shivering and vasoconstriction will occur

The Hypothalamus as a water/salt balance regulator:

• Osmoreceptors check the salt balance of the blood

• if blood is too salty, the person will sense thirst and ADH will be released to retain water

The Hypothalamus’s function in hunger and GI motility:

• Sensors determine blood sugar and fat levels in the blood

• If blood sugar is too low: person will feel hungry

• if blood sugar is too high: Satiety will be sensed

• Can also increase the activity and digestion of the GI tract during feeding

Other functions of the hypothalamus:

• Sleeping and wakefulness, sexual response, emotions, and endocrine functions

• all affected by specific nuclei within the hypothalamus

What are the four main functions of the hypothalamus?

• Feeding

• Fighting

• Fear

• Sex