Chapter 13 - Bones and Integrating Reflexes

Compact bone

external layer of used for support

Spongey bone

internal layer made of calcified lattice

Epiphysis

end of a long bone

Epiphyseal plate

site of bone growth

Diaphysis

shaft of long bone

2 main composition of bone

collagen + calcium phosphate hydroxyapatite

What structure does the collagen make (in the structure of bone)

triple-helix structure —> makes the bone stronger than steel

Trabecular bone supplied by

bone ECF

Compact bone supplied by

blood vessels in Haversian canals

Chondrocytes form

cartilage

Osteoblasts create

calcium phosphate crystals to replace cartilage

role of EC matrix Ca2+

forms calcified matrix of bone and teeth

role of ECF Ca2+

- Neurotransmitter release at synapse
- muscle contraction in heart and smooth muscle
- blood clotting (coagulation)
- helps stick cells together (tight junctions)
- regulates neuron excitability

role of ICF Ca2+

- triggers muscle contraction (binding to troponin)
- acts as second messenger

PTH secreted by the

parathyroid glands

PTH function

INCREASES blood Ca2+

target cells of PTH

kidney, bone, intestine

target receptor of PTH

membrane receptor acts via cAMP

absence of PTH causes

hypocalcemic tetany (lack of Ca2+)

Calcitriol other name

Vitamin D3

calcitriol

activated form of vitamin D (from sunlight) helps regulate Ca2+ levels in the body by INCREASING blood Ca2+

transport method of PTH

dissolved in plasma

transport method of Vitamin D3

bound to plasma protein

What triggers calcitriol production

- low plasma Ca2+
- PTH indirectly increases by activating kidney enzymes
- Prolactin (during pregnancy)

Target cells of calcitriol

intestine, bone, kidney

How does PTH act on intestine?

stimulates calcitriol production —> increases Ca2+ absorption (stimulation of transport protein)

How does calcitriol + PTH act on bone?

enhances osteoclast activity —> increase of Ca2+ release from bone

How does calcitriol act on kidney?

increases Ca2+ reabsorption; prevents calcium loss in urine

Which tissue does calcitriol directly impact?

intestine

transport method of calcitonin

dissolved in plasma

target receptor of calcitonin

G protein-coupled membrane receptor

Target cell/tissue of calcitronin

bone and kidney

target receptor of calcitrol

nuclear

calcitronin secreted by the

C cells of thyroid gland (parafollicular cells)

What triggers release of calcitonin

high plasma [Ca2+]

function of calcitonin

LOWERS BLOOD CA2+
- prevents bone resorption
- enhances kidney excretion (through urine)

mass balance for calcium balance

dietary intake should equal Ca2+ loss in the urine and feces

ECF calcium concentration

2.5mM

what regulates calcium uptake by bone

calcitonin

what regulates calcium release by bone

PTH, Calcitriol, Cortisol

Where is the main storage for calcium

bone

what regulates calcium transport into cells

electrochemical gradients

what regulates calcium transport out of cells

active transport

what regulates calcium uptake by kidney

passive filtration

what regulates calcium release by kidney

PTH

calcitonin function for kidney

increases calcium excretion —> loss in urine

What is responsible for bone resorption?

Osteoclasts

Osteoclast function

secrete acid and enzymes that dissolve calcium phosphate in bone —> release of Ca2+ into blood

Osteoporosis

bones to become weak and brittle due to excessive resorption

Monosynaptic reflex has

a single synapse between the afferent and efferent neuron

Polysynaptic reflex has

at least one interneuron between sensory and motor neuron; has both synapses in the CNS

RECALL: Sensory neurons are afferent or efferent neurons?

afferent neurons

RECALL: Motor neurons are afferent or efferent neurons?

efferent neurons

Which reflex is slower?

polysynaptic reflex because of the additional synapse

RECALL: where is the CNS located?

spinal cord

location of interneuron on polysynaptic reflex

CNS/spinal cord

skeletal muscle reflexes are

monosynaptic and polysynaptic

autonomic reflexes are

ALL polysynaptic

somatic reflexes control

skeletal muscles

autonomic reflexs control

smooth msucle, cardiac muscle, and glands

autonomic reflexes have at least two synapses in

the CNS and autonomic ganglion

reciprocal inhibition

when one muscle contracts while its antagonist relaxes

what happens during knee-jerk reflex?

activation of quadriceps (contraction)
inhibition of hamstrings (relaxation)

what type of reflex is the activation of quadriceps in knee-jerk?

monosynaptic

what type of reflex is the inhibition of hamstrings in knee-jerk?

polysynaptic

two types of stretch receptors

golgi tendon organs and muscle spindles

golgi tendon organ links the

muscle and tendon together

golgi tendon organ function

prevents excessive contraction to prevent injury

golgi tendon organs (GTO) detects

changes in muscle tension

what detects the increase in tension for GTO

sensory nerve endings embedded in colalgen fibers (of TENDON)

GTO reflex monosynaptic or polysynaptic?

polysynaptic

What is the main characteristic of muscle spindles?

they are tonically active

tonically active meaning

fires even when muscle is at rest

muscle spindle detects

changes in muscle length and stretch

what does muscle spindle function

regulation of muscle tone

extrafusal fibers

main muscle fibers that generate force

purpose of muscle spindles being tonically active

muscle readiness

more stretch = _________ sensory neuron firing

faster

Crossed Extensor Reflex monosynaptic or polysynaptic?

polysynaptic

Crossed extensor reflex function

maintains balance when one leg is lifted (in response to pain)

Crossed extensor reflex paired with

withdrawal reflex

which leg shows flexion response during crossed extensor reflex

leg with pain stimulus

which leg shows extension response during crossed extensor reflex

leg without pain stimulus (holding leg)

muscle action during flexion response

flexor muscles contract
extensor muscles inhibited

muscle action during extension response

flexor muscles inhibited
extensor muscles contract

sensory receptors send input to

spinal cord, brainstem, cerebellum, and cerebral cortex

vestibular system sends signals to

cerebellum

spinal reflexes sends signal to

spinal cord

which main components control postural reflexes?

cerebellum and brainstem (spinal cord)

role of cerebellum in voluntary movement

Provides feedback and corrects errors in movement

role of motor cortex in voluntary movement

Sends commands to muscles to execute movement

role of basal ganglia in voluntary movement

Helps refine movement and prevent unwanted motions

role of cortical association areas in voluntary movement

Plans and organizes movement