CHP 14 Brain and Brainstem

Gray matter

-collection of neurosomas, dendrites, and synapses

-forms the surface layer (cortex) over cerebrum and cerebellum

-forms nuclei deep within the brain

-dull color due to little myelin

White Matter

-Bundles of Axons

-white color from myelin around nerve fibers

-composed of tracts (bundles of axons) that connect one part of brain to another and to the spinal chord

Ventricles

-four internal chambers within the brain; two lateral ventricles, third ventricle (superior), fourth ventricle (inferior) that connects to the central canal

-the cerebral aqueduct connects 3rd and 4th

-lines by Ependymal

-contains the choroid plexus that supplies capillaries

Choroid Plexus

spongy mass of blood capillaries on the floor of each ventricle

-covered by ependymal

Ependymal

type of neuroglia that lines ventricles and covers choroid plexus

produces cerebrospinal fluid

Cerebrospinal fluid

clear, colorless liquid that fills the ventricles and canals of CNS

production of cerebrospinal fluid

-begins with filtration of blood plasma through capillaries of the brain

-ependymal cells modify the filtrate

-now there is more sodium and chloride than plasma, less calcium+glucose+ and VERY LITTLE protein

Functions of Cerebrospinal fluid

1) Buoyancy =. floats so brain doesn’t rest of cranial floor

2) Protection = protects brain from striking the cranium when head is jolted

3) Chemical stability = flow of CSF rinses away metabolic wastes from nervous tissue, chemical homeostasis

Flow of cerebrospinal fluid

start in lateral ventricle

through the third ventricle

through the cerebral aqueduct

through the fourth ventricle

through the central canal

into the subarachnoid space

extra fluid leaves through the arachnoid villi (“holes”) where it is filtered back into the dura mater sinuses

Blood Supply to brain

brain is only 2% of body weight but gets 15% of blood

neurons have a high demand for ATP so needs oxygen + glucose supplied from blood

Brain Barrier System

regulates what substances can get from the bloodstream into the tissue fluid of the brain

two entries protected: blood capillaries of brain tissue + capillaries of choroid plexus

characteristics of Blood brain barrier system

-consists of tight junction between cells: everything must go through a cell and not between them

-highly permeable to water, glucose, and lipid soluble substances (oxygen, carbon dioxide, alcohol, caffeine, nicotine etc)

-can be an obstacle for letting medications through

-trauma + inflammation cna causę damage and allow pathogens to enter through

Reticular formation

-loose web of gray matter that runs vertically through all levels of the brainstem

-has connections with many areas of cerebrum

Functions of the Reticular Formation

1) somatic motor control= adjust muscle tension, gaze centers (allow fixation), central pattern generators (neural pools that produce rhythmic signals to muscles of breathing and swallowing)

2) cardiovascular control

3) pain modulation/blockage

4) sleep and consciousness (circadian rhythm)

5) habituation

Cerebellum

“little brain”

contains more than half of all brain neurons (because mostly gray matter), the branching white matter is the arbor vitae

function of cerebellum

motor coordination and locomotion

mostly subconscious

Parts of Forebrain

-Diencephalon= top of brain stem

-Telencephalon= cerebrum

Diencephalon parts

-thalamus

-hypothalamus

-epithalamus

Thalamus

-different parts do different things, 23 different nuclei

-”the front desk/gateway to the cerebral cortex (gray matter covering on the cerebrum) = the thalamic nuclei filters information on the way to the cerebral cortex

-motor control = feedback loop between cerebral cortex and basal nuclei

-memory and emotional functions of limbic system

Hypothalamus

-control center of autonomic nervous system + endocrine system

-essential for homeostasis

Basic Functions:

• Hormone secretion (pituitary gland)

• Autonomic effects (the subconscious things; heart rate, blood pressure, etc)

What attaches the hypothalamus to the pituitary gland

Infundibulum (a stalk)

Main functions of the hypothalamus

-thermoregulation

-food and water intake (thirst/hunger feels)

-sleep + circadian rhythms

-memory (short term to long term)

-emotional behavior and sexual response (the big feelings)

Epithalamus

-very small mass of tissue composed of the pineal gland, habenula (bridge from the limbic system to the midbrain)

Cerebrum (Telencephalon)

-largest part of the human brain

-sensory perception, memory, thought, judgement, voluntary motor actions

-five lobes named after the cranial bones overlying them

How are the left and right cerebral hemispheres connected

-the longitudinal fissure (superficial)

-corpus callosum = white matter tract (deep)

What feature determines amount of cranial activity/”smartness”

gyri (ridges)

sulci (indentations)

“more wrinkles = smarter brains”

What are the five lobes

frontal

parietal

occipital

temporal

insula (deepest one)

note: functions spread out across multiple lobes

Cerebral White Matter

most of the cerebrum is this

includes tracts (bundles of nerve fibers) in the central nervous system

Three types of Cerebral White Matter Tracts

1) Projection Tracts

2) commissural tracts

3) association tracts

Projection Tracts

-extend vertically between higher and lower brain and spinal cord centers

association tracts

connect different regions within the same cerebral hemisphere

Commissural tracts

cross from one cerebral hemisphere to the other allowing for communication between the two sides of the cerebrum

*the corpus callosum

Gray Matter

-neural integration

located:

Cerebral Cortex (outer covering of the cerebrum)

Limbic System

Basal Nuclei

Cerebral Cortex

-covers the surface of the cerebrum

-contains billions of neurons

-gray matter found here

Neurons of the Cerebral Cortex

Stellate Cells = many dendrites projecting off the neurosomas, receive sensory input + process that information

Pyramidal Cells = thick dendrite w many branches that have dendritic spines, only neuron that leaves the cortex and connects with other parts of the CNS

Limbic System

-the center of emotion and learning

-circular feedback, can cause over activation “big feelings”

-have both gratification (pleasure or reward) + Aversion (fear or sorrow)

Cingulate Gyrus

of the limbic system

arches over corpus callosum in frontal ad partial lobes

Hippocampus

of the limbic system

for memory functions (short term to long term)

Amygdala

of the limbic system

for emotional functions

Basal Nuclei

masses of cerebral gray matter deep within the white matter

involved in motor control

sends signals back and forth between itself and the midbrain + cortex

3 brain centers of the basal nuclei

-caudate nucleus

-putamen

-globus pallidus

Lentiform

the putamen and globus pallidus together

Integrative Functions of the Brain

higher brain functions such as:

• sleep

• memory

• congnition

• emotion

• sensation

• motor control

• language

combining parts of brain working/integrated together

functions of the brain do not have easily defined anatomical boundaries

How do we perceive sensation?

1) Primary Sensory Cortex = where sensory input is first received and you become conscious of the stimuli

2) Association Areas process and interpret the sensory info

• Primary Visual Cortex= make sense of what we see

• Multimodal Association areas = take in multiple senses and combine them into an overall perception of our surroundings

Overall what are special senses?

limited to the head and employ relatively complex sense organs

can an earth worm do it?

What are the special senses? list

1) Vision = visual primary cortex in occipital lobe + visual association area

2) Hearing = Primary auditory cortex in temporal lobe & insula + auditory association area

3)Equilibrium = Cerebellum + several brainstem nuclei + association cortex

4) Taste = “Gustatory” primary gustatory cortex in the post central gyrus in the parietal lobe

5) Smell = “Olfactory” primary olfactory cortex in the temporal lobe/frontal lobe

What are general senses?

“somatic senses”

“Primary Somatosensory cortex”

• distributed over the entire body and use simple receptors

• touch, pressure, stretch, movement, heat; cold, pain

How do we perceive our general senses?

1) head = cranial nerves carry info, body= ascending tracts bring info

2) Thalamus processes the input from contralateral side

3) We become aware when it reaches the POST CENTRAL GYRUS DUE TO the Somesthetic association area

Sensory Homunculus

a diagram of the primary somesthetic cortex

resembles an upside down sensory map of the contralateral side of the body

Somatotophy

point to point correspondence between an area of the body and an area of the CNS

Steps of Motor Control

1) Association (Premotor) area in the frontal lobes is where we plan to move

2) Transmitted to neurons of PRECENTRAL GYRUS (primary motor area)

3) send to brainstem and spinal chord which leads to muscle contraction

Neurons of the Precentral Gyrus for Motor control

1) Pyramidal Cells = upper motor neurons

• the fibers from upper motor neurons synapse w lower motor neurons whose axons then go to the skeletal muscles for contraction

Somatotopy of the pre central gyrus

motor homunculus is distorted because the amount of cortex devote to a given body region is the number of muscles/ motor unites and not the body region size

What are basal nuclei and how do they help motor control

• control repetitive movements (ex: walking), start/stop of intentional movement, and learned behaviors/habits (ex: driving a car)

• FEEDBACK LOOP between cerebrum to basal nuclei to thalamus back to cerebrum

Dyskinesias

Dys = abnormal

kines = movement

damage to basal nuclei causes this which causes abnormal movements

How does the cerebellum help with motor control

• motor coordination

• muscle tone and posture

• joints working together coordination

Ataxia

damage to the cerebellum can cause this

clumsy, awkward gait

Language is caused by what areas

1) Wernicke Area

• posterior to lateral sulcus usually in left hemisphere

• RECOGNITION of spoken and written language

• formulates phrases sends that “plan” to Broca area

2) Broca Area

• inferior prefrontal cortex usually in left hemisphere

• creates the MOVEMENT for speaking and signing

• sends to primary motor cortex to lower motor neurons that grab the right muscles

3) Affective Language Area

• usually right hemisphere

• inflection in voice

Aprosody

damage to the affective language area

causes flat emotionless speech

Aphasia

a language deficit from damage to the hemispheres with Wernicke and Broca areas

Types of Aphasia

1) Nonfluent (broca) aphasia

• slow speech, slurring, words sound wrong, and difficulty choosing words

2) Fluent (wernicke aphasia)

• speech normal but it’s all gibberish

3) Anomic Aphasia

• can speak and understand speech but cannot identify words or pictures

Cerebral Lateralization

= the difference in the structure and function of the cerebral hemispheres

• Left = categorical, analytical, spoken/written language

• Right = representational, artistic, imagination, patterns, sense comparisons

Cerebral Lateralization in correlation to handedness, age, sex

-Right Handed = left hemisphere categorical in 96%

-Left Handed = left hemisphere categorical in 70%, right hemisphere categorical for 15%, neither for other 15%

-males more lateralization than females

Cranial Nerves Usage

how the brain communicates with the rest of the body

12 pairs of cranial nerves

exit the cranium through foramina

mainly send to organs in head and neck

Pathways of Cranial Nerves

1) Motor neurons start in nuclei of brainstem and go to glands and muscles, sensory fibers start in receptors in head and neck and go to brainstem

2) most carry fibers between brainstem and ipsilateral (same side) receptors and effectors, EXCEPT optic nerve and trochlear nerve that sometimes do decussation

Classification of Cranial Nerves

Sensory = I, II, VIII

Motor = III, IV, VI, XI, XII

Mixed = V, VII, IX, X

Olfactory Nerve

(I)

send sense of smell to the brain

Optic Nerve

(II)

send visual signals to the brain by the optic chiasma

Oculomotor Nerve

(III)

control size of pupil and movement of the eye

Trochlear Nerve

(IV)

movement of the eye

Trigeminal Nerve

(V)

LARGEST cranial nerve

most important sensory nerve of the face

3 divisions:

• Ophthalmic Division (sensory)

• Maxillary Division (Sensory)

• Mandibular Division (mixed)

Abducens Nerve

(VI)

movement of eye left and right

Facial Nerve

(VII)

Motor (facila expressioms, salviary glands, palatine glands ) + sensory (taste on the tongue0

What does damage to facial nerve (VII) cause

saggy facial muscles

no sweet or salty taste

Vestibulocochlear Nerve

(VIII)

sense of equilibrium and sound

Glossopharyngeal nerve

(IX)

control tongue, salivary glands, swallowing muscles

Vagus Nerve

(X)

“wandering” nerve

most extensive distribution of any cranial nerve

control cardiac, pulmonary, digestive, and urinary function

swallowing, speech, viscera regulation

damage to vagus nerve causes what

hoarseness and loss of voice

impaired swallowing

fatal if both are cut

Accessory nerve

(XI)

movement of the sternocleidomastoid and trapezius (move head and neck)

Hypoglossal Nerve

(XII)

movement of the tongue

Senescence of nervous system

peak development at age 30

brain weights 56% less by age of 75

cortex thinner, gyro narrower, sulci wider, fewer synapses and neurotransmitters/receptors

short term memory suffered most

autonomic nervous system less efficient at regulating body temp ad blood pressure

Alzheimers

nervous disability of old age

plaques of fibrillar proteins (amyloid) appear