Anatomy Final

Major divisions of the Nervous System — Anatomical

Central nervous system: Composed of the brain and spinal cord, responsible for processing and integrating information

Peripheral nervous system: Includes all nerves outside the CNS. It consists of the sensory (afferent) and motor (efferent)

Major divisions of the Nervous System — Functional

Sensory (afferent) division: Transmits sensory information to the CNS (e.g., touch, pain, temperature)

Motor (efferent) division: Carries commands from the CNS to muscles and glands. It has 2 main branches:

-Somatic Nervous System: Controls voluntary muscle movements

-Autonomic Nervous System (ANS): Regulates involuntary functions, such as HR and digestion, with sub-divisions:

1) Sympathetic Nervous System: Prepares the body for “fight or flight” responses

2) Parasympathetic Nervous System: Controls “rest and digest” activities

Gray Matter vs White Matter

Gray Matter

Structure: Composed of neuron cell bodies, dendrites, and glial cells

Function: Involved in processing and integrating information (e.g., sensory processing, decision-making, memory). Found mainly in the cortex of the brain and in areas like the nuclei of the spinal cord

White Matter

Structure: Composed of myelinated sheaths around CNS axons

Function: Facilitates rapid transmission of electrical signals different regions of the CNS. Found deeper in the brain and along the tracts in the spinal cord.

Differences

Glial cells support neurons structurally and functionally, contributing to the formation of the blood-brain barrier, myelination, immune defense, and the regulation of neuronal environments. Dysfunction in glial cells can lead to neurodegenerative or impaired neuronal communication

Parts of Multipolar Neuron (order of polarity)

-Dendrites (receiving end- negative polarity)

-Cell body (soma) (Central part- negative polarity)

-Axon hillock (transition point- negative polarity)

-Axon terminals (transmission path- positive polarity)

How parts of multipolar neuron work together

-Dendrites receive signals from other neurons and transmit electrical impulses toward the cell body. The signals are usually in the form of graded potentials

-The cell body (soma) integrates the incoming signals, which are either excitatory or inhibitory. If the summation of these signals reaches a threshold, an action potential is generated

-The axon hillock is the area where the action potential is initiated if the threshold is crossed

-The axon conducts the action potential (electrical signal) away from the cell body toward the axon terminals

-The axon terminals release neurotransmitters that transmits signals to other neurons or effector cells (muscle, glands)

Types of glial cells and their functions

CNS Glial Cells

-Astrocytes: provide structural support, regulate blood blood-brain barrier, and maintain ion balance

-Oligodendrocytes: form myelin sheaths around CNS axons

-Microglia: act as immune cells in the CNS, clearing debris

-Ependymal cells: Line ventricles of the brain and produce cerebrospinal fluid (CSF)

PNS Glial Cells

-Schwann cells: form myelin sheath PNS axons

-Satellite cells: surround neuron cell bodies in ganglia, proving support and nutrient exchange

Why they’re critical:

Glial cells support neurons structurally and functionally, contributing to the formation of the blood-brain barrier, myelination, immune defense, and the regulation of neuronal environments. Dysfunction in glial cells can lead to neurodegenerative diseases or impaired neuronal communication

Major functions of the nervous system

-Sensation: the detection of stimuli (e.g., temperature, pain, light) through sensory receptors

-Integration: processing sensory input in the CNS to formulate a response

Example

-Sensation: pain receptors in the skin detect the heat and send signals to the CNS

-Integration: the brain processes the signal and decides that the stimulus is dangerous

-Response: the brain sends a signal to the muscles to withdraw the hand

Resting membrane potential

-ion channels and pumps: the sodium-potassium pump (Na+/K+ pump) moves 3 Na+ ions out of the cell and 2 K+ ions into the cell, creating an electrochemical gradient

-ion concentrations: more Na+ ions are outside the neuron and more K+ ions are inside

-Leaky potassium channels: potassium ions leak out of the neuron through specific channels, contributing to a more negative internal environment

-Membrane permeability: the neuron’s membrane is more permeable to K+ than to Na+, which helps establish the resting potential of about -70mV

Action Potential

-Depolarization: a stimulus causes Na+ channels to open, allowing Na+ ions to flow into the neuron. This makes the inside of the neuron less negative (more positive)

-Threshold: if the membrane potential reaches the threshold (around -55mV), an action potential is triggered

-Action potential: Na+ channels open rapidly, and the inside of the neuron becomes positive (around +30mV). This is called depolarization

-Hyperpolarization: the membrane potential becomes more negative than the resting potential before stabilizing back to rest

Role of ion movement

-Na+ influx: causes depolarization, leading to the action potential

-K+ efflux: returns the membrane to resting potential (repolarization)

Graded potentials

-Excitatory postsynaptic potentials (EPSPs): depolarize the membrane (make it less negative) bringing the neuron closer to the threshold for an action potential

-Inhibitory postsynaptic potentials (IPSPs): hyperpolarize the membrane (make it more negative), moving the neuron further away from the threshold

-Graded in size: the amplitude of graded potential is proportional to the strength of the stimulus and can be either excitatory or inhibitory

How graded potentials influence AP generation

-EPSPs increase the likelihood of reaching the threshold for an action potential, where IPSPs decrease the likelihood

-A neuron will fire an action potential when the sum of EPSPs and IPSPs at the axon hillock reaches the threshold

-Graded potentials are critical for modulating the sensitivity of neurons to incoming signals

Neurotransmitters

Amino acids

-Glutamate: excitatory, involved in learning and memory

-GABA: inhibitory, helps regulate neural excitability and prevents overstimulation

Biogenic amines

-Dopamine: can be excitatory or inhibitory, involved in motivation, reward, and motor control

-Serotonin: mostly inhibitory, regulates mood, sleep, and appetite

-Norepinephrine: primarily excitatory, involved in arousal and stress responses

Peptides

-Endorphins: inhibitory, act as natural painkillers

-Substance P: excitatory, involved in transmitting pain signals

Acetylcholine

-Cholinergic: can be excitatory (in skeletal muscles) or inhibitory (in the heart)

Fibrous Joint

Characteristics

-Bones united by collagen fibers

Types

1) Suture

2) Syndesmosis

3) Gomphosis

Mobility

1) Synarthrosis (immobile)

2) Ampiarthrosis (slightly mobile)

3) Synarthrosis (immobile)

Cartilaginous joint

Characteristics

-Bones united by ends united by cartilage

Types

1) Synchondrosis (hyaline)

2) Symphysis (fibrocartilage)

Mobility

1) Synarthrosis (immobile)

2) Amphiarthrosis (slightly moveable)

Synovial joints

Characteristics

-Bone ends covered with articular cartilage and enclosed with a capsule line with a synovial membrane

Types

1) Plane

2) Hinge

3) Pivot

4) Condyloid

5) Saddle

6) Ball and socket

Mobility

All diathrosis (freely moveable)

Excitation-contraction coupling

1) Stimulus is detected

2) Action potential generated is propagated along the sarcolemma and down the T tubules

3) Action potential triggers Ca2+ release from terminal cisternae of SR

4) Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed

5) Contraction; myosin cross bridges alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process

6) Removal of Ca2+ by active transport into the SR after the action potential ends

7)Tropomysoin blockage restored blocking actin active site; contraction ends and muscle fiber relaxes

Twitch

a single stimulus is delivered; the muscle contracts and relaxes

Wave summation

stimuli are delivered more frequently, so that the muscle does not have adequate time to relax completely and contraction force increases

Unfused (incomplete) tetanus

more complete twitch fusion occurs as stimuli are delivered more rapidly

Fused (complete) tetanus

a smooth continuous contraction without any evidence of relaxation

Resting membrane potential (-60 to -90mV)

-Concentrations of ions tries to maintain homeostasis, but the cell can’t. Why not? Because the cell membrane is selectively permeable, preventing full equilibrium.

-At rest, K+ crosses membrane easily and Cl- and Na+ do not

-A- (negatively charged protein particles) can’t pass through

-Na+/K+ pump moves three Na+ out and two K+ in using energy

Action potential (explosion of electrial activity)

-Occurs when a neuron sends a depolarizing current down an axon, away from the cell body

-Stimulus causes the resting potential to move towards 0mV

-Threshold: -55mV

-All or none principle

Order of channels opening/closing

1) Sodium channels open

2) More sodium channels open (voltage-gated sodium channels) AT THRESHOLD

3) Sodium channels close

4) Potassium channels open

5) Potassium channels close

Skeletal mucles contraction

1) Myosin heads hydrolyze ATP and become reoriented and energized

2) Myosin heads, bind to actin forming crossbridges

3) Myosin heads rotate toward center of the sarcomere (power stroke)

4) As myosin heads bind ATP, the cross bridges detach from actin

Direct phosphorylation

Energy source: CP (creatine phosphate)

Oxygen use: none

Products: 1 ATP per CP, creatine

Duration of energy provided: 15 seconds

Anaerobic pathway

Energy source: glucose

Oxygen use: none

Products: 2 ATP per glucose, lactic acid

Duration of energy provided: 30-40 seconds, or slightly more

Aerobic pathway

Energy source: glucose; pyretic acid; free fatty acids from adipose tissue; amino acids from protein catabolism

Oxygen use: required

Products: 32 ATP per glucose, CO2, H2O

Duration of energy provided: hours

Hypertrophy

Hormones, stress, steroids can increase production

Atrophy

Decreased use, diseases can reduce production

Ascending (afferent) pathway

Carries peripheral sensations UP to the brain

Descending (efferent) pathway

Carries motor commands DOWN toto the skeletal muscles

Ganglion

In CNS: called nucleus

Sympathetic Nervous System

-Fight or flight

E= exercise, excitement, emergency, and embarrassment

Parasympathetic Nervous System

-Rest and digest