anatomy module 2

chapters 10-15

myocyte

muscle cell; muscle fiber

sarcolemma

the plasma membrane of the muscle fiber

sarcoplasma

the cytoplasm of a muscle fiber

sarcoplasmic reticulum

ER of a muscle fiber

functional characteristics of all muscle

• contractibility: ability to shorten and generate force

• excitability: ability to respond to stimuli by producing electrical signals

• extensibility: ability to stretch without being damaged

• elasticity: ability to return to its original length/shape following distension

functions of muscle

• movement

• posture and joint stabilization

• open/close body passages

• thermogenesis

thermogenesis

• contracting skeletal muscles produce heat

  • voluntary/involuntary; shivering

• contracting smooth muscles also helps prevent heat loss

  • goosebumps, dartos muscle

connective tissue components of skeletal muscles

• sheaths of CT hold skeletal muscle tightly together in parallel alignment so they can generate force as a whole

• provides elasticity

epimysium

connective tissue around the whole muscle

fascicle

• bundle of muscle fibers

• wrapped by perimysium

endomysium

betwen individual muscle fibers

tendons

• CT attachment of a skeletal muscle to a bone’s periosteum

• continuous with all 3 CT sheaths of muscle beyond the length of the fibers

aponeurosis

broad, flat tendon

origin

attachment of muscle on the stationary/less moveable bone

insertion

attachment of muscle on the mobile/more moveable bone

direct attachment

• connective tissue very short

• muscle may appear to be attached to the bone

• less common

indirect attachment

• connective tissue forms tendons/aponeurosis

• common

strains vs. sprains

• strains: muscle and/or tendons

• sprains: ligaments

nervous innervation of muscle

• each muscle is typically innervated by a single nerve which branches extensively within the CT sheaths

• each axon making up the nerve synapses with multiple muscle cells

blood supply of muscles

• each muscle is typically supplied by a single artery which branches extensively within the CT sheaths

• capillary networks within the endomysium are wavy in resting muscle to allow for extensibility

skeletal muscle fiber striation

due to the organization of proteins found within muscle cells

myofibrils

• specialized contractile organelles

• specific for myocytes; allow muscles to contract

• made up of three types of proteins

  • contractile, regulatory, structural

sacromere

• the basic contractile unit of muscle

• several units make up the myofibril

contractile proteins

• actin and mysoin myofilaments

• do the work; occur in all cells

thin filament

• actin, tropomyosin, troponin

• actin attached to Z disc; extends to center

• actin molecules arranged in a double helix

• each actin molecule has a myosin-binding site for the myosin head

thick filament

• many myosin molecules

• tethered to Z disc by titin

  • provides slack

• myosin heads attach to actin in the thin filaments, then pull thin filaments inward

actin and myosin arrangement in sacromere

• Z disc (line): separates sacromeres

• A band: entire length of thick filament

• M line: center of the sacromere

• I band: thin filament only

• H zone: thick filament only

regulatory proteins

• tropomyosin: covers myosin-binding sites

• troponin: holds tropomyosin strand together

• when calcium ions bind to troponin, it changes its shape, pulling tropomyosin off the binding site

structural proteins

• titin: inside sacromere; anchors myosin to Z disc

  • allows for extensibility

• dystrophin: at the ends of the myofibril to keep it in place

sarcoplasmic reticulum

T-tubule

• invagination of sarcolemma

• carries an electrical impulse from surface membrane deep into muscle fiber

tubules of the SR

network of tubules that regulate calcium ion levels and where electrical signals travel down

terminal cisterns of the SR

• the tubules of the SR coming to an end

• where calcium ions are stored and released

sliding filament mechanism of contraction

Ca+ released from terminal cisterns SR and binds to troponin → troponin is released from tropomyosin → tropomyosin on actin rolls over → myosin heads bind and pivot to pull the thin filaments inward

change in filaments during contraction

• do not change in length; only amount of overlap changes

• A-band doesn’t change

motor unit

• one nerve fiber and all the muscle fibers innervated by it

  • branches out to a number of fibers

• each muscle fiber is supplied by only one motor neuron

  • one fiber will not be innervated by multiple nerves

the neuromuscular junction (NMJ)

communication site b/w neuron and muscle cell

three main components of the NMJ

• axon terminal: aka terminal bouton

• junctional folds of the sarcolemma: increase surface area for more receptors

• synaptic cleft: space b/w folds and axon terminal

nerve impulse to movement

LOOK AT NOTES FOR AFTER #3!!!!!

skeletal muscle fiber types

• slow oxidative type I

• fast ox-glycolytic type IIa

• fast-glycolytic type IIb/IIx

slow oxidative type I characteristics

• myoglobin content: high

• contraction velocity: slow

• metabolic process for ATP production: aerobic

• fatigue resistance: high

• color: red

• fiber diameter: small

slow oxidative type I function

• maintaining posture and endurance activities

• constant states of contraction

fast ox-glycolytic type IIa characteristics

• myoglobin content: high

• concentration velocity: fast

• metabolic process: aerobic + anaerobic

• fatigue resistance: intermediate

• color: pink

• fiber diameter: intermediate

fast ox-glycolytic type IIa function

walking, sprinting

fast-glycolytic type IIb/x characteristics

• myoglobin content: low

• contraction velocity: fast

• metabolic process: anaerobic

• fatigue resistance: low

• color: white

• fiber diameter: large

fast-glycolytic type IIb/x function

• rapid, intense movements of very short duration

• more force (bc of large fiber)

arrangement of fascicles in muscles

• within a fascicle, all muscles fibers are parallel to one another

• arranged differently in various muscles

• arrangement reflects function

  • longer fibers: greater range of motion

  • shorter fibers: greater strength

fascicles and muscles shapes

strength of a muscle and the direction of its pull are determined partly by the orientation of its fascicles

circular

• fascicles arranged in concentric rings

• always found around external body openings (sphincters)

convergent

origin is broad and the fascicles converge toward a tendon of insertion

pennate

short fascicles that attach obliquely (angulary) to a tendon that runs the length of the muscle

parallel

• fascicles run parallel to the long axis of the muscle

• fusiform and straplike (sartorius)

lever systems

• effort: force being produced by contracted muscle

  • based on insertion point

• load: external weight/body part; resistance

• fulcrum: pivot/fixed point; where movement stems from

first class lever

fulcrum in the middle

second class lever

load in the middle

third class lever

effort in the middle

muscles actions and interactions

• a muscle that crosses a joint, acts at that joint

• muscles only pull

• muscles that produce opposite actions lie on opposite sides of a joint

  • agonist: contracts to cause an action

  • antagonist: stretches and yields to the effects of the agonist

synergist

• acts to assist an agonist by adding extra force or reducing undesirable movements

  • canceling out unwanted movements

• fixators: fixes a bone in place

naming skeletal muscles

• named according to several descriptors

• location, shape, size, fascicle arrangement, location of attachments, number of origins, action

• often, multiple criteria are used

flexion

a muscle that crosses on the anterior side of a joint

extension

a muscle that crosses on the posterior side of a joint

abduction

a muscle that crosses on the lateral side of a joint

adduction

a muscle that crosses on the medial side of a joint

muscle compartments of the limbs

• fascial compartments group muscles of similar origin and function

• most compartments are innervated by a single named nerve

fascia

connective tissue separating compartments

anterior brachial compartment

• muscles: coracobrachialis, brachialis, biceps brachii

• action: flexion of shoulder and elbow

• innervation: musculocutaneous nerve

posterior brachial compartment

• muscles: triceps brachii, anconeus

• action: shoulder and elbow extension

• innervation: radial nerve

anterior antebrachial compartment

• muscles: superficial, intermediate, and deep flexors

• action: flexes wrist and fingers

• innervation: median or ulnar nerve

  • ulnar innervates pinky and half of ring finger

posterior antebrachial compartment

• muscles: superficial and deep extensors

• action: extends wrist and fingers

• innervation: radial nerve

anterior thigh compartment

• muscles: quadriceps femoris

• action: knee extension and hip flexion

• innervation: femoral nerve

posterior thigh compartment

• muscles: hamstrings

• action: knee flexion and hip extension

• innervation: tibial nerve (portion of sciatic nerve)

medial thigh compartment

• muscles: adductors

• action: hip adduction and medial rotation, and slight knee flexion

• innervation: obturator nerve

anterior leg compartment

• muscles: tibialis anterior, EHL, EDL, fibularis tertius

• action: dorsiflexion, inversion, extension of toes

• innervation: deep fibular nerve

lateral leg compartment

• muscles: fibularis longus and brevis

• action: plantar flexion and eversion

• innervation: superficial fibular nerve

superficial posterior leg compartment

• muscles: gastrocnemius and soleus

• action: knee flexion and plantar flexion

• innervation: tibial nerve

deep posterior leg compartment

• muscles: tibialis posterior, flexor digitorum longus, popliteus, flexor hallucis longus

• action: plantar flexion, knee flexion, toe flexion

• innervation: tibial nerve

compartment syndrome

• when muscles swell from trauma/overuse, pressure in the compartment increases

• compressed vessels → ischemia, swelling

  • ischemia: blockage of blood flow

• compressed nerves → pain or numbness

• can require a fasciotomy

the nervous sysem

• master controlling and communicating system

• rapid and specific signals

• immediate responses

• employs electrical signals and chemical means to send messages from cell to cell

endocrine system

• communicates by means of chemical messengers (hormones) secreted into the blood

• slow acting

3 overlapping functions of the nervous system

• sensory function

• integration function

• motor function

sensory function

sensory receptors monitor changes inside and outside the body

integration function

CNS receives and interprets sensory input and makes a decision for action

motor function

motor neurons elicits responses by activating effector organs

divisions of the nervous system

• central nervous system

• peripheral nervous system

central nervous system

• brain and spinal cord

• integrative and control centers

peripheral nervous system

• all nervous tissue outside the CNS

• cranial and spinal nerves that can have sensory or motor functions

• connects the CNS to the rest of the body

divisions of the PNS

• sensory (afferent) division

• motor (efferent) division

sensory division

• somatic and visceral sensory nerve fibers

• conducts impulses from receptors to the CNS

motor division

• motor nerve fibers

• conducts impulses from the CNS to effectors (muscles and glands)

systems of the motor division

• somatic nervous system

• automatic nervous system (ANS)

somatic nervous system

• somatic motor (voluntary)

• conducts impulses from the CNS to skeletal muscles

automatic nervous system

• visceral motor (involuntary)

• conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands

divisions of the automatic nervous system

• sympathetic division

• parasympathetic division

sympathetic division

• mobilizes body systems during activity

• fight or flight response

parasympathetic division

• conserves energy

• promotes house-keeping functions during rest

• rest and digest

nervous tissue

composed of neurons (excitable) and neuroglia (non-excitable)

special characteristics of neurons

• conductivity: able to send electrical signals from one body part to another

  • called action potentials/nerve impulses

• extreme longevity: neurons can live and function for a lifetime

• do not divide: cannot replace themselves if destroyed

  • few exceptions

• high metabolic rate: require constant supply of O₂ and nutrients

the basic neuron