Anatomy Exam 4

Thick filament is made of

250 myosin molecules

Myosin head

Binding site for actin and ATP

ATPases

• Located on myosin heads

• Catalyzes the hydrolysis of ATP to form ADP and P

Thin filament is made of

Actin

Tropomyosin

The wound around the actin

Troponin

Molecules that are bound to tropomyosin and contain calcium binding sites

G actin (globular)

Free individual protein building blocks

F actin

Long assembled polymer chains

Sarcoplasmic reticulum function

Store calcium ions

L tubules

Extend longitudinally into the terminal cisternae that encircle myofibrils

T tubules

Extensions of the cell membrane that penetrate into the center of the myofiber

Triads

Formed by a T tubule with a terminal cisterna on either side

T tubule function

Allow electrical impulses traveling along the sarcolemma to move deeper into the cell and stimulate the SR to release calcium

Motor neuron

A neuron who’s cell body is located in the brain or the spinal cord

Function of an axon

Projects outside of the spinal cord to control the skeletal muscles

Neuromuscular junction

A site where a motor neuron’s terminal meets the muscle fiber

Anatomy of a neuromuscular junction

1. Presynaptic terminal

2. Synaptic cleft

3. Postsynaptic membrane

Axon terminal

The presynaptic terminal that contains synaptic vesicles that contain acetylcholine

Synaptic cleft

Space between the nerve terminal and the sarcolemma that contains acetylcholinesterase enzymes

Acetylcholinesterase function

Responsible for the catabolism of released ACh so that its effects are not prolonged.

Postsynaptic membrane

Characterized by a high concentration of ACh and membrane invaginations

Sarcolemma

The membrane of the skeletal muscle cell

Junctional folds

Contain acetylcholine receptors in the postsynaptic membrane

Calcium function

Binds to troponin to cause contraction

Motor unit

Group of muscle fibers in a muscle that are innervated by a single motor neuron

Small motor unit

A single motor neuron that supplies a small number of muscle fibers. Permits fine motor control of the muscle.

Large motor unit

A single motor neuron that supplies a large number of muscle fibers. Concerned with gross movements.

Nervous system function

1. Sensory input

2. Integration

3. Motor response

Sensory input

Comes from the many sensory receptors that monitor changes occurring both inside and outside the body

Integration

The sensory input is sent to the CNS, which determines

Motor response

Nervous system sends signals via motor output to muscles or glands to initiate the response

Subdivisions of the nervous system

1. CNS

2. PNS

CNS

Brain and spinal cord

PNS

Vast network of spinal and cranial nerves that are linked to the brain and spinal cord

Neuroglia in the CNS

• Microglia cells

• Astrocytes

• Ependymal cells

• Oligodendrocytes

Neuroglia found in the PNS

• Schwann cells

• Satellite cells

Microglia

Act as macrophages, clearing cellular debris and dead neurons from nervous tissue through phagocytosis

Astrocytes function

• Regulate the extracellular ionic concentration

• Provide a blood brain barrier

• Repair

Most abundant glial cell in the CNS

Astrocytes

Astrocytes regulation of ionic concentration

Removes excess potassium

Blood brain barrier

Prevents the entry of large sized particles, ions, or proteins from blood into the extracellular material of the brain

Astrocytes role in repair

Repair neuronal tissue in the CNS

Ependymal cells

Type of neuronal support cell that forms the epithelial lining of the ventricles in the brain and the central canal of the spinal cord

Oligodendrocytes

Myelinate the CNS. One can myelinate multiple neuronal axons

Voltage gated calcium channels function

The bridge between the electrical signals of the motor neuron and the chemical signal that triggers the muscle contraction

Ligand gated channels in the junctional folds

Convert a chemical neurotransmitter signal into an electrical signal across the muscle cell membrane

ACh in the junctional folds

Binds to receptors in the folds that opens the channels and causes an influx of sodium unto the muscle cell

voltage gated channels in the junctional folds

Translate chemical signals into electrical impulses

Myelin

Insulating layer made of lipid material and protein that spiral wraps around nerves

Schwann cell

Wraps around a single axon to myelinate an axon of the PNS

Node of Ranvier

Periodic gap in the insulating sheath of the axon on certain neurons that facilitate rapid conduction of impulses

Saltatory conduction

The jumping of impulses from node to node

Neuron

Basic working unit of the brain that transmits information to other nerve cells, muscles, or glands

Number of neurons at birth

100 billion

Neuron regeneration

Does not occur. they are not replaced once they die

Neuron cell body (soma)

Contains the nucleus, maintains the neuron’s structure, and provides energy to drive activities

Axon

Long extension carrying information away from the cell body

Axon hillock

Where the axon and cell body join

Dendrites

Carries information towards the cell body

Nucleus

Cell bodies located within the CNS

Ganglion

Cell bodies located outside the CNS

Electrical gradient of the cell

There are slightly more negative charges than positive charges inside the cell. Therefore, excess ions collect along a thin shell on the inner and outer surfaces of the plasma membrane.

Extracellular concentration of Na+ (mM/L)

150

Intracellular concentration of Na+ (mM/L)

15

Extracellular concentration of K+ (mM/L)

5

Intracellular concentration of K+ (mM/L)(mM/L)

150

Relative permeability of Na+

1

Relative permeability of K+

50-75

Resting membrane potential

Excess number of charges inside the cell and excess number of charges outside the cell

Resting membrane potential (mV)

-60 - -90

Resting neuron

Membrane is polarized (more negative on the inside)

Depolarized

When the inside of the membrane becomes more positive

Hyperpolarized

When the membrane potential becomes more negative than it is at resting potential

Importance of potassium

Establish resting potential that is closest to the resting membrane potential. The most permeable ion

Na+/K+ pumps

Contribute a small amount to the negative voltage.

Action potential

A temporary shift from negative to positive in the neuron’s membrane potential

Gated sodium and potassium channels during rest

All closed

Sodium during depolarization

Flow into the negatively charged axon

Repolarization

The return of the membrane potential towards its negative resting value

Channels during repolarization

• Na+ channels become inactivated

• K+ channels open

Channels during hyperpolarization

• K+ channels stay open a little longer

• Na+/K+ pumps reestablish the resting potential

All or nothing principle

If a stimulus exceeds the threshold potential, the nerve or muscle fiber will give a complete response otherwise no response will occur

Propagation

Occurs because voltage-gated Na+ channels are opened. Electrical signals are rapidly conducted from one node to the next and initiates another action potential

Refractory period

The amount of times it takes for an excitable membrane to be ready to respond to a second stimulus

Absolute refractory period

Interval of time during which a second action potential cannot be initiated, not matter how large a stimulus

Relative refractory period

Interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before

Synapses

Form between axon terminals on the presynaptic neuron and the cell body of dendrites or dendrites of the postsynaptic neuron

Excitatory postsynaptic potential

Makes the inside of the cell more positive, brining the membrane potential closer to its threshold

Inhibitory postsynaptic potential

Makes the inside of the cell more negative, bringing the membrane potential farther from the threshold

Components of the brain

• Cerebrum

• Diencephalon

• Brain stem

• Cerebellum

Cerebrum

• Divided into the right and left cerebral hemispheres by the longitudinal fissure

• Communicate with each other through the corpus callosum

• The largest uppermost portion of the brain and accounts for two thirds of the total weight

Gyri and sulci

To increase the surface area of the brain so more neurons can be present

Fissures

The deep furrows of the brain

Sulcus

The shallow furrows of the brain

Gyri

The ridges between the sulci

Lobes of the cerebrum

• Frontal lobe

• Parietal lobe

• Occipital lobe

• Temporal lobe

Grey matter

Contains numerous cell bodies and few myelinated axons

Whit matter

Contains relatively few cell bodies and is composed chiefly of myelinated axons

2 lateral ventricles

• Connects to third ventricle through interventricular foramen

• Lie within their respective hemispheres of the cerebrum