CHS anatomy chapter 7

Sensory input

one of the main functions of the nervous system; gathering information;Uses millions of sensory receptors to monitor changes occurring inside and outside the body(Afferent)

•These changes are called Stimuli

Satellite cells

Protect and cushion the cell bodies of nerves; lollipop shape

Integration

one of the main functions of the nervous system; processes and interprets the sensory input and decides if action is needed

afferent

to go towards

efferent

to move from

motor output

one of the main functions of the nervous system; It affects a response to the integrated stimuli; The response activates muscles or glands(Efferent pathway)

Central Nervous system(CNS)

Organs- located in the dorsal cavity

*Brain

*Spinal cord

•Function: Integration; command center

*Interpret incoming sensory information

*Issues outgoing instructions

Peripheral Nervous System(PNS)

•Nerves extending from the brain and spinal cord

*Spinal nerves - carries impulses to and from the spinal cord

*Cranial nerves - carries impulses to and from the brain

•Functions: Serves as a line of communication among sensory organs, the brain and spinal cord, and glands or

muscles

Sensory division

Nerve fibers that carry information to the central

nervous system from sensory receptors located in

various parts of the body

•Keeps the CNS informed of the events inside & outside

the body(afferent)

somatic sensory fibers

deliver impulses from the skin, muscles and joints. (Somatic cells – Body cells)

Visceral Sensory Fibers

deliver impulses from the visceral or internal organs

Motor division (efferent - “ to move from”)

Nerve fibers that carry impulses away from the CNS to effector organs such as muscles and glands

somatic nervous system

Voluntary NS

•Consciously controls skeletal muscles

Autonomic nervous system

Involuntary NS

•Automatically controls smooth and cardiac muscles and glands

•Further divided into:

1. Parasympathetic – allows the body to “unwind”

2. Sympathetic - mobilizes the body during

extreme situations

glia or glial cells

supporting cells in the central Nervous system; grouped together are called neuroglia which means nerve glue; their general functions are to support, insulate, protect

Even though some of the glial cells resemble neurons, they are unable to transmit nerve impulses

*Unlike neurons, glial cells retain their ability to undergo mitosis

Astrocytes

Abundant, star-shaped cells that account for nearly half of

the neural tissue

•Their numerous projections have swollen ends that brace

the neurons and anchor them to their blood capillaries

•Forms a living barrier between neurons and their capillaries,

regulating what passes between the two blood brain barriers

•Prevents harmful substances from passing into the neuron

•Controls the chemical environment of the brain by “mopping

up” any K+ ions and neurotransmitters that have leaked

out.

microglia

Spiderlike phagocytes

•Monitor the health of nearby neurons

•Dispose of debris, including bacteria and dead brain cells

Ependymal cell

Lines the central cavities of the brain called Ventricles and spinal cord

•Their beating cilia helps circulate the Cerebrospinal Fluid (CSF) that fills the cavity and cushions the CNS

Oligodendrocytes

Glia which wraps its flat extensions around nerve fibers in the

central nervous system

•Produces fatty insulating covering called Myelin Sheaths(for the CNS)

satellite cells

supports the PNS; •Protect and cushion the cell bodies of nerve

Schwann cells

Form myelin sheath (White Matter) around nerve fibers in the peripheral nervous system

cell body

nucleus and metabolic center of the cell

•Contains a transparent nucleus with large nucleolus

•The cytoplasm surrounding the nucleus contains all

of the typical organelles Except Centrioles – amitotic

Neurons

also referred to as Nerve Cells, are

highly specialized to transmit messages or impulses from

one part of the body to another

Nissl bodies

for the cell body; specialized rough endoplasmic reticulum and filaments which maintain the cells’ shape called Neurofibrils

Processes

fibers that extend from the cell body

Ex. The nerve that spans from the lumbar vertebrae to

the big toe

•These processes are located outside the cell body

Dendrites

conduct impulses toward the cell body

•Neurons may have hundreds of these

Axons

conduct impulses away from the cell body; may occasionally form collateral branches along their length, but form hundreds to thousands of branches along their terminal end called Axon terminals

Axon Hillock

The Neurons have only one axon arising from the cone like region (like the neck) of the cell body

Neurotransmitters

Axon terminals have hundreds of tiny vesicles or membrane sacs containing

Synaptic cleft

The neurotransmitters travel across a neuron gap called

the

synapse

The junction between nerves & other nerves is called a

Myelin sheath

whitish, fatty material covering axons

•Myelin protects and insulates the fibers and increases the transmission rate of nerve impulses.

Schwann cells

myelin around the axons of the PNS

Neurilemma

the plasma membrane of the myelin sheath

Nodes of Ranvier

gaps in the myelin sheath along the axon in the PNS

Ogliodendrocytes

myelin sheaths around axons of CNS

Multiple sclerosis (MS)

The myelin sheaths around the fibers are gradually destroyed & converted into hardened sheaths called Scleroses; There is no cure, but injections of Beta interferon and Corticosteroids appears to slow the progression of the disease

*Possibly Autoimmuine

Gray matter

collections of cell bodies and unmyelinated fibers

Nuclei

clusters of cell bodies within the CNS; apart of gray matter

white matter

collections of myelinated fibers

Tracts

bundles of nerve fibers in the CNS; apart of the white matter

Ganglia

collections of cell bodies of the PNS

Nerves

bundles of nerve fibers of the PNS

Sensory(Afferent) neurons

Carry impulses from the sensory receptors to the CNS

special sense receptors

vision, smell & hearing

Cutaneuous receptors

simple sense organs of the skin including light & deep pressure and pain receptors

Visceral receptors

internal organs

proprioceptors recieptors

detect stretch or tension of muscles and tendons

•The cell bodies of the sensory neurons are always

located in the ganglion outside the CNS in the PNS

•Keeps us informed about what is going on inside and

outside the body

Interneurons

Located in neural pathways in the central nervous system

•Connects sensory and motor neurons of the neural pathway

motor (Efferent) neurons

Carry impulses from the central nervous system to viscera,

muscles, or glands

•Usually ends in numerous axon terminals which will synapse

with a muscle or gland or another neuron

•Their cell bodies are usually located in the CNS but their

axon is located outside the CNS

multipolar neurons

many extensions from the cell body

•All motor and interneurons are multipolar

•Most common structure

unipolar neurons

have a short single process leaving the cell body which divides immediately into a proximal(central) process and a distal (peripheral) process together forming the axon

•This is the only time Axons carry impulses towards and away

from the cell body

•Sensory neurons found in PNS ganglia are unipolar

lamellar corpuscle

deep pressure receptor

meissners corpuscle

touch receptor

Irritablility

Ability to respond to stimuli and convert it to a nerve impulse

conductivity

Ability to transmit the impulse to other neurons, muscles and glands

Repolarization

Immediately after the Sodium ions rush into the neuron, the

membrane permeability changes again (becoming impermeable to Na) and now the Potassium ions rush out of the neuron, which Repolarizes the membrane

depolarization

A stimulus causes the neuron’s membrane channels to open,

becoming permeable to sodium ions

•As the sodium (Na +) flows inside, the membrane becomes

more positive inside & more negative outside

•The membrane is now Depolarize

polarized

Fewer positive ions are inside the cell than outside the cell

•As long as the inside remains more negative than the

outside, the neuron will remain inactive

propagation of an action potential

If enough sodium enters the cell, the action potential is

propagated over (moves along) the entire axon

•This is an “all or nothing” response

•Impulses travel faster when fibers have a myelin sheath

“depolarization”

1. A nerve impulse leaves the spinal cord and travels along the axon until it reaches the Axon terminals of the motor neuron

2. This causes the Calcium Channels of the terminals to open

allowing calcium ions to enter the axon terminal

3. The calcium ion entry causes the synaptic vesicles in the

axon terminal to release their contents (acetylcholine) into

the synaptic cleft by the process of exocytosis

Acetylcholine diffuses across the synaptic cleft and attaches

to receptors (membrane proteins) on the sarcolemma of the

muscle cell

5. In response to the binding of ACh to a receptor, the

sarcolemma becomes temporarily permeable to sodium (Na+)

•This allows Sodium ions to rush into the muscle cell and

simultaneously potassium ions to leave the cell, but at a

slower rate, causing an excess of positive ions inside.

•This is the reverse of the typical electrical conditions of the

muscle cells.

•Usually there is an excess positive charge on the outside

of the cell (sarcolemma) due to the Sodium/Potassium

pump (3 Na +out / 2 K +in)

This depolarization of the muscle cell is referred to as an Action potential

The action potential will then travel the entire length of the sarcolemma conducting the electrical impulse from one end of the muscle cell to the other

The result is a Contraction of the muscle Once started, a specific muscle contraction cannot be stopped

6. Once the action potential has begun, Ach begins to be broken down into Acetic Acid and Choline by the enzyme AChE orAcetylcholinesterase

Therefore a single nerve impulse produces only one contraction of the muscle cell

Nuerotransmitter

chemical released by nerve upon arrival of nerve impulse in the axon terminal

Reflex

rapid, predictable, and involuntary response or a stimulus

Reflex arc

direct route from a sensory neuron, to an interneuron, to an motor neuron (effector)

somatic reflexes

Reflexes that stimulate the skeletal muscles

•Example: pull your hand away from a hot object

Autonomic reflexes

Regulate the activity of smooth muscles, heart & glands

•Example:Regulation of smooth muscles of the pupils to constrict when a bright light shines in your face.

The five elements of a reflex

1. Sensory receptor - reacts to a stimulus

2. Sensory neuron - carries message to the integration center

3. Integration center (CNS) - processes information and directs motor output

4. Motor neuron - carries message to an effector

5. Effector organ - is the muscle or gland to be stimulated

Two-neuron reflex arcs

•The Simplest type of reflex arc

•Example: Patellar (knee-jerk) reflex

•The Quadricep attached to the hit tendon extends

•Tested during a physical exam to determine the

health of the nervous system

Three-neuron reflex arcs

•Example: Flexor (withdrawal) reflex.

•When a limb is withdrawn from a painful stimulus

CNS developing

The CNS develops in the embryonic from a simple tube called the Neural Tube

•The neural tube extends down the dorsal median plane of the embryo

•By the 4th week the neural tube expands and Brain

formation begins.

•The remaining neural tube which lies posterior to the brain develops into the Spinal Cord

•The central canal of the neural tube enlarges and becomes the 4 chambers or Ventricles within the brain

•These ventricles are filled with cerebrospinal fluid (CSF)

Cerebrum

Composed of two Cerebral Hemispheres, collectively

•Paired (left and right) superior parts of the brain

•Includes more than half of the brain mass

•As the cerebral hemispheres develop and grow, they enclose and obscure most of the brain stem.

-Much like a mushroom cap covers the stalk

•The entire surface is made of ridges called Gyri ( gyrus), shallow grooves called Sulci (sulcus) and deeper grooves called Fissures

Diencephalon

in deep into the brain; between the cerebrum and brain stem

Brain stem

stem on the bottom of the brain where the spinal cord can connect to

Cerebellum

above the brain stem

•Frontal lobe

•Parietal lobe

•Occipital lobe

•Temporal lobe

Surface lobes of the Cerebrum

Cerebral Cortex

•The outermost layer of the cerebrum is composed of Gray Matter and contains the Cell Bodies of the neurons responsible for all of the following functions: -Voluntary movement -Interpretation of Sensation -Memory -Logical & Emotional Response -Consciousness -Speech

Primary somatic sensory area

•Impulses from the body’s sensory receptors are localized and interpreted in this area of the brain

•Allows you to recognize pain, coldness or a light touch

•The sensory pathways are crossed and the left hemisphere receives impulses from the right side of the body

•Located in parietal lobe posterior to the Central Sulcus

Sensory Homunculus

The spatial map that illustrates the location of these body regions on the cortex

Primary Motor Area

Allows us to consciously move our skeletal muscles

•Located anterior to the central sulcus in the frontal lobe

•The axons of these motor neurons form the major voluntary motor tract called the Corticospinal or Pyramidal Tract which descends to the spinal cord

•Most of these neurons control our fine motor skills like: Movements of the face, mouth and hands

Broca’s area

Involved in our ability to speak

•Located at the base of the precentral gyrus which is

located anterior to the central sulcus

•Located on only one of the cerebral hemispheres

•Damage to this area results in the inability to say words properly

Anterior Association Area

•This area is involved in higher intellectual reasoning and socially acceptable behavior

•**Is responsible for problem solving and language comprehension (on next page of notes)

•Located in the anterior part of the frontal lobe

Posterior Association Area

This area stores complex memories

•It plays a role in recognizing faces, patterns and blending several inputs to help us understand whole situations.

Wernicke’s Area

Located at the junction of the temporal, parietal & occipital lobes; Allows you to sound out words.

• Located on only one of the cerebral hemispheres

• The language comprehension area is located in the frontal lobe

Corpus Callosum

is a very large fiber tract which is located in the white matter and arches above the brain stem

•It connects hemispheres and allow them to communicate with each other

•This is important because some of the functional cortical area are located in one hemisphere or the other

Commissures

The large fiber tract for the Corpus Callosum

Association Fiber tracts

connect areas within the same hemisphere

Projection Fiber Tracts

connect the cerebrum with the lower CNS centers. (Corticospinal/Pyramidal)

- A band of these fibers is called the Internal Capsules

Basal Nuclei

islands of gray matter buried within the white matter of the cerebral hemispheres

- Also called Basal ganglia

- Helps regulate voluntary motor activities by modifying instructions being sent to the skeletal muscles by the primary motor cortex

- Particularly important in starting and stopping movements

Huntington’s Disease

A genetic disorder controlled by a single dominant allele located on Chromosome 4

CAG Codons which code for Glutamine:

Normally 11-30 codons; Huntington’s 40-80 codons

*Symptoms typically begin during middle age.

*Leads to the degeneration of the Basal nuclei and eventually the cerebral cortex

*Symptoms include: irritability, forgetfulness, wild jerky movements, swallowing & speech problems, and eventually mental deterioration

Parkinson’s disease

Typically strikes people in their 50’s and 60’s

*A degenerative disease which causes deterioration of the neurons in the midbrain which release Dopamine(a neurotransmitter that makes us feel good or happy)

*The lack of Dopamine causes the Basal Nuclei to become overactive.

*Symptoms include: Tremors, Stiff facial expressions and Trouble getting their muscle going

1. Thalamus

2. Hypothalamus

3. Epithalamus

What are the three major structures of the Diencephalon?

Thalamus

Surrounds the shallow third ventricle of the brain

•It is a relay station for sensory impulses passing upward to the sensory cortex

•Transfers impulses to the correct part of the cortex for localization and interpretation; (We have TWO)

Hypothalamus

Lies directly under the thalamus & makes up the floor of the Diencephalon

•Important autonomic nervous system center

•Helps regulate body temperature

•Controls water balance

•Regulates metabolism

*Helps your body maintain Homeostasis

(Have only ONE of these)

•It is also the center for many drives and emotions and therefore

it is part of the Limbic system or “emotional brain”

•Contains: thirst, appetite, sex, pain & pleasure centers

•It regulates the nearby Pituitary gland

Pituitary Gland

hangs from the anterior floor of the hypothalamus by a slender stalk

•a endocrine gland which produces two hormones: oxytocin - stimulates contractions of the uterus and milk “let down” for nursing; antidiuretic hormone (ADH) - Promotes retention of water by the kidneys

•The Mammillary bodies are located on the floor of the hypothalamus posterior to the pituitary gland and are the reflex centers involved in olfaction (smell)

Epithalamus

Forms the roof of the third ventricle

•Houses the Pineal body, an Endocrine gland which produces the hormone Melatonin - regulates our sleep cycle. Makes us drowsy at night and it is at its lowest level at midday

•It also includes the Choroid plexus of the third ventricle which a knot of capillaries that forms cerebrospinal fluid

The capillaries of the choroid plexus supply raw plasma need to make CSF,

BUT- - - ependymal cells make the actual CSF

Choroid plexus

is a network of capillaries found inside the ventricles

Brain Stem

It is a pathway for ascending and descending tracts

•It contains many small areas of gray matter whose nuclei produce the rigidly programmed autonomic behaviors necessary for survival like breathing & blood pressure

•Attaches to the spinal cord.

Midbrain

Small part of the brain stem composed mostly of tracts of nerve fibers

•It extends from the mammillary bodies to the pons inferiorly

Cerebral aqueduct

•A tiny canal travels through the midbrain which connects the third ventricle of the diencephalon to the fourth ventricle below; IN THE MIDBRAIN

Cerebral peduncles

Anteriorly(in the midbrain), it has two bulging fiber tracts which convey ascending and descending impulses