A&P Ch. 12 The Central Nervous System

The central nervous system is composed of

the brain and the spinal cord

Functions of the CNS

• integration/interpretation of incoming sensory information

• sending out a motor response to effector organs

Four regions of the brain

1. Cerebrum

2. Diencephalon

3. Brain Stem

4. Cerebellum

Gray Matter

the dendrites, cell bodies, and axon terminals (unmyelinated axons)

all synapses are found in, messages passed from one neuron to another

White Matter

myelinated axons

passes messages between different areas of gray matter, sending messages from one part of CNS to another

Where gray matter and white matter are in the brain

gray matter is peripheral (surrounding, outside), white matter is central (inside)

Cerebral cortex

outer layer of gray matter in the brain

where gray and white matter are found in the brain stem

scattered gray matter is found within white matter

where gray and white matter are found in the spinal cord

gray matter is found in a butterfly pattern surrounded by white matter

Central canal

in spinal cord, found in center of gray, butterfly pattern, matter- serves spinal cord with CSF

Ventricles of the CNS

chambers filled with cerebrospinal fluid- chambers share CSF with each other, connected

2 lateral ventricles

one in each cerebral hemisphere, ram horns

Third ventricle

found in diencephalon, right underneath lateral ventricles

Fourth ventricle

found in hindbrain, most inferior ventricle

connects to third ventricle via cerebral aqueduct

continuous with central canal of spinal cord

Cerebral Hemispheres

form the most superior portion of the brain, make up most of brain by mass

has three regions

wrinkled in appearance

Three general regions of the cerebral hemispheres

1. cerebral cortex

2. white matter

3. basal nuclei

How cerebral hemispheres have wrinkled appearance

Gyri- ridges

Sulci- spaces between, shallow grooves

this creates more surface area, better integration, why humans are so smart

Longitudinal fissure

separates the left and right hemispheres

Transverse cerebral fissure

separates the cerebral hemispheres from the cerebellum

Cerebral cortex

part of cerebral hemispheres, provides self awareness, sensation, communication, memory, understanding/learning, initiation of voluntary movement, decision making, whole personality

has three functional areas

Three functional areas of cerebral cortex

1. Motor areas- controls voluntary movement

2. Sensory areas- conscious awareness of sensations- figuring our what sensation/ what body part

3. Association areas- integrate diverse information, linking something experience in moment to something in the past

Hemispheres are Contralateral

one cerebral hemisphere controls the other side of the body

Motor areas of the cerebral cortex

controls voluntary movement

consists of:

1. primary motor cortex

2. premoter cortex

3. Broca’s area

4. frontal eye field

Primary motor cortex

allows for conscious control of skilled/precise voluntary movements, initiates + controls most of the body

consists of pyramidal cells

Pyramidal cells

large neurons found in primary motor cortex, heavily myelinated

• axons travel to spinal cord in corticospinal tracks (bundles of axons)

• synapse with and stimulate motor neurons- send info to muscle tissue

Motor homunculus

the body is represented spatially in the primary motor cortex of each hemisphere- the amount of space in brain a body part takes up

the larger the body part, the more neurons are dedicated to that region of the body on the cortex

fine tune the control of that body part

Premotor cortex

helps plan movements by selecting and sequencing basic motor movements into more complex tasks- must communicate with primary motor cortex, without this the primary motor cortex would not execute movement

controls voluntary actions that depend on sensory function- move body parts according to senses, ex: walk without running into anything

Frontal eye field

controls voluntary movement of the eyes, moving gaze

Broca’s Area

directs muscles in/around mouth involved in speech production

becomes active as we prepare to speak, plan other voluntary motor activities- lips, tongue, cheek

is only found on one side of the brain- on left side for most people

Sensory areas of the cerebral cortex

allows for conscious awareness of sensation

there are 8 areas

Primary somatosensory cortex of cerebral cortex

receives information from the general sensory receptors (any sense not in the head)

if damaged, hard to perceive touch + recognize objects

Sensory homunculus

the body is represented spatially according to site of stimulus input

the larger the body part, the more neurons are dedicated to that area of the body on the cortex

Somatosensory association cortex of the cerebral cortex

integrates sensory input relayed to it via primary somatosensory cortex, produces understanding of what is being felt (size, texture, relationship of its parts)- stores memory so can recognize when touched again

Visual Areas (sensory area) of cerebral cortex

1. Primary visual cortex- receives visual information that originates on the retina in the eye

2. Visual association area- uses past visual experiences to interpret visual stimuli → allows us to recognize what we see

largest region of cerebral cortex~ really depend on it

Auditory Areas (sensory area) of cerebral cortex

1. Primary auditory cortex- interpretation of sound from inner ear as pitch, loudness, location

2. Auditory association area- permits perception of sound stimulus + stores memories of sounds for reference- recognize sounds heard before

Vestibular cortex of cerebral cortex

allows for conscious awareness of balance/orientation

Primary olfactory cortex of cerebral cortex

allows for conscious awareness of different odors

Gustatory cortex of cerebral cortex

allows for perception of taste stimuli

Visceral sensory area of cerebral cortex

allows conscious perception of visceral sensations- don’t usually feel visceral organs as long as they are functioning normally- want to know if organ is overstretched (ex: bladder, stomach)

Lateralization

a division of labor exists between two hemispheres

Cerebral dominance

one hemisphere dominates a particular tast

usually in reference to language→ left side

• left side of brain: language abilities, math, logic

• right side of brain: visual-spatial skills, insightful, empathetic, creative

Fiber tracts

connect the right and left sides of the brain, can share information almost instantaneously, and allows complete functional integration (sides communicating)→ better refines abilities of each side

Cerebral White matter of Cerebrum

allows for communication in CNS, lies deep to cortical gray matter

Classification of cerebral white matter (fibers)

1. Association fibers- connect different areas of the same hemisphere

2. Commissural fibers- connect corresponding areas of different hemisphere- allows hemispheres to operate at coordinated team

3. Projection fibers- allows sensory information to reach cortex and motor output to leave cortex- project to spinal cord and go to the other side of body

Basal Nuclei of Cerebral Cortex

clusters of synapses, “basal ganglia”

filters out incorrect or inappropriate responses relating to muscle movement, and emotions and cognition

deep to the white matter in each cerebral hemisphere

Deincephalon

part of the brain made up of the thalamus, hypothalamus, and epithalamus

Thalamus

most superior of diencephalon, relays sensory information coming into the cerebral cortex- sorts incoming info and sends to right place

information is “edited” here, impulses with similar functions are grouped together and relayed to appropriate part of cortex

like the brain’s mailman

motor activities, cortical arousal (sleep/wake cycles), learning, memory

Hypothalamus

main visceral control center of the body- regulates activity of internal organs

• controls autonomic nervous system

• initiates physical response to emotion- limbic system (emotional brain) involvement→ involved in perception of fear, rage, libido

• regulates body temp- the body “thermostat”

• regulates food intake- monitors blood nutrient levels

• regulates water balance and thirst- monitors concentration of body fluids

• regulates sleep-wake cycles- uses daylight/darkness cues from visual pathways

• controls endocrine system function- controls secretion of hormone by other glands

Epithalamus

where Pineal gland (pineal body) is- secretes melatonin hormone

helps regulate sleep-wake cycle

less light → more melatonin produced

Brain Stem

• produces rigidly programmed, autonomic behaviors, necessary for survival (involuntary, life-sustaining behaviors)

• provides pathway for fiber tracts running from higher brain centers to lower brain centers and spinal cord

• innervation of the head- 10 of 12 pairs of cranial nerves are associated

Three parts of the brain stem

1. the midbrain

2. the pons

3. the medulla oblongata

The Midbrain

of the brain stem, regulates motor movement, regulate hearing and vision, alertness, temperature control

The Pons

of the brain stem, *respiratory control (do not have to think about respiratory rate), bladder, control, swallowing, most functions associated with attached cranial nerves

The Medulla Oblongata

of the brain stem, meets with spinal cord

• Cardiovascular center: regulates heart rate and blood pressure (so involuntary)

• Respiratory rate: controls respiratory rhythm, depth of breath (not too shallow or deep)

• others: regulation of vomitting, swallowing, coughing, sneezing

Cerebellum

1. receptors in body relay information to cerebellum about body position + where body is in space- motor cortex sends info here about intent to move

2. cerebellar cortex “decides” best way to execute movement- force, direction, and extent of muscle contraction

• allows smooth, coordinates, movement required for everyday life

Functional Brain Systems

networks of neurons that span multiple regions of the brain and work together to accomplish one or more related tasks

The Limbic System

responsible for emotions

Amygdala (Amygdaloid Body)

region of limbic system, takes incoming sensory info and responds to perceived threats with fear or aggression, fight or flight response

Cingulate gyrus

region of limbic system, expressing emotions through gestures (hands + face), resolving mental conflicts during times of frustration- prevent from acting extremely

Psychosomatic illness

illness with physical symptoms that results specifically from emotional causes

ex: being excited or nervous causes increase in heart rate

because limbic system output is relayed through hypothalamus and hypothalamus is the main visceral organ control center

Prefrontal cortex

what limbic system interacts with, where info ends up after going through hypothalamus, decision making, social skills, personality, cognitive skills

intimate relationship between our thoughts and our feelings:

• react emotionally to things we consciously understand to be happening

• are consciously aware of our emotions

communication between limbic system and prefrontal cortex explains

1. why emotions sometimes override logic

2. why reason can stop us from expression emotion inappropriately

Reticular Activating System Functions

1. sends continuous stream of impulses (APs) to the cerebral cortex→ cerebral cortex is kept alert and excitability is enhanced

2. Filters out repetitive, familiar, or weak signals→ prevention of sensory overload, dumps unimportant info so we aren’t aware of it

Higher mental functions of the brain

1. Language

2. Memory

Regions responsible for language

• left side of the brain mainly

• Broca’s area- mostly left side, production of speech

• Wernicke’s area- language comprehension, speaking clearly, correct sentence structure

corresponding language area of right hemisphere functions

• understanding and interpreting nonverbal components of language- body language

• understanding emotional components of language- understand emotion by tone

Memory

the storage and retrieval of information/past experiences

Short term memory

working memory, stores small amounts of information for short periods of time

ex: what you ate for dinner last night

Long term memory

stores large amounts of information for longer periods of time

not necessarily permanent

Transfer from STM to LTM requires:

1. Emotional state: heightened emotional state leads to almost instantaneous memory formation and storage

2. Rehearsal: repeating information enhances memory- practice

3. Association: the ability to learn and remember the relationship unrelated items- linking two pieces of info, ex: using mnemonics

4. Automatic memory: unconscious formation of memory in LTM- no obvious reason, just remember it

Declarative memory

learning explicit formation (facts), involves ability to manipulate symbols and language

Nondeclarative memory

memory required though repetition - difficult to unlearn, usually based on performance rather than recollection→ ex: riding a bike

Forms of protection of the brain

1. Skull

2. Meninges

3. Cerebral Spinal Fluid

4. Blood Brain Barrier

Meninges

membranes that surround and protect the brain, covers + protects CNS, blood vessels around the brain, contains CSF

made up of three layers of connective tissue

Duramater

most external layer meninge, “tough mother” → thickest + strongest layer

has two sublayers:

• periosteal layer: attaches to inner surface of skull bones- tough, fibrous layer, helps hold other layers and brain in place

• meningeal layer: forms true external covering of brain

Arachnoid mater

deep to dura mater meninge, “spider mother”- looks like a spider web

beneath membrane is subarachnoid space - csf filled space

in between brain and skull bone

Pia mater

innermost meningeal layer, “gentle mother”, thinnest layer

highly vascularized layer- holds blood vessels in place → brain gets nutrients

like cling wrap around the brain

Cerebralspinal Fluid

liquid surrounding brain + spinal cord

liquid cushion → protects brain from physical trauma

gives buoyancy to CNS structure- brain floats

nutrient and chemical messenger carrier- neurons always need glucose, carries neurotransmitter to regulate brain activity

Blood Brain Barrier

what separates neurons from blood, provides a constant environment for CNS tissue operation

tight junctions between cells that create capillary walls, astrocytes surrounding capillary→not a lot of free movement between blood supply and neurons, keep that constant environment, more selective permeability, brain still need to dispose waste

Simple diffusion across BB barrier

allows lipid-soluble substance to pass freely- fatty acids and respiratory gases

Specific transport of BB barrier

• facilitated diffusion- glucose, amino acids, specific ions

• Transcytosis- forms vesicle, moves large substances in/out of tissue, insulin, iron

Substances not allowed through BB barrier

blood borne metabolic waste (nitrogenous waste), proteins, certain toxins, most drugs, nonessential amino acids, potassium ions

Variability of BB barrier

some parts of the brain need easy access to blood to measure variables in order to maintain homeostasis

ex: vomiting center, hypothalamus

Concussions

alteration in neuron functioning following a physical blow to the head, temporary, but multiple can result in cumulative damage

Contusions

permanent neurological damage resulting from bruising of the brain

Spinal cord functions

1. Conduction pathway- carries impulses between the brain and the body

2. Major reflex center- spinal reflexes are initiated and completed at the spinal cord level, drives entire reflex, not the brain

Protection of the spinal cord

1. vertebrae

2. meninges- just one layered dura mater, arachnoid mater, and Pia mater

3. cerebrospinal fluid

Spinal cord extends

from the foramen magnum to L1-L2, not all the way down

Conus medullaris

tapered, cone-shaped structure where spinal cord ends

Filum terminale

fibrous extensions that extend from conus medullaris to coccyx, anchors spinal cord in place

• dural and arachnoid membranes continue past conus medullaris to the sacral vertebrae→ allows CSF to keep going to lower structures

Width of spinal cord is consistent in length except

cervical and lumbar enlargements where serves serving upper and lower limbs arise- needs to be a little wider to branch off to arms and legs

Number of spinal nerves

31 pairs of PNS attach to spinal cord

Causa equina

collection of nerve roots at the end of the vertebral canal, nerves that extend off conus medullaris serve lower parts

Dorsal horns

projections of gray matter on the dorsal side of the spinal cord, consists of interneurons (highly specialized)

receives somatic and visceral sensory input- sending info to brain

Ventral horns

projections of gray matter on the ventral side of the spinal cord, consists of interneurons and somatic motor neurons (for skeletal muscle tissue)

for motor output

Lateral horn

projections of gray matter found only in thoracic and superior lumbar segments

contains motor neurons that serve visceral organs- help regulate organ activity

Ventral roots

where axons of the ventral horn motor neurons (efferent fibers) exit the spinal cord, can be somatic or visceral→ axons of ventral and lateral horns leave here

Dorsal roots

what axons of sensory receptors (afferent fibers) enter the spinal cord- info travels towards brain

can be somatic or visceral

Dorsal root ganglia

swelling of a portion of the dorsal root where cell bodies of sensory neurons are found

Spinal nerves

formed by dorsal and ventral roots fusing