Human Bio 2 Exam

Lecture 9 (Slide 11) - Last Lecture

What does the autonomic system involuntarily control?

cardiac and smooth muscles, organs, glands

what are the 2 divisions of the autonomic NS

sympathetic and parasympathetic NS

what is used for each ANS impulse

two neurons (preganglionic and postganglionic ) and one ganglion for each impulse

when is our sympathetic division active

situations where we may be required to fight or flight

where do most preganglionic fibres (SNS) arise and what do they terminate

middle portion of spinal cord

terminate ganglia that lie near the cord

Why does the sympathetic division increase heartbeat and dilate airways?

For a ready supply of glucose and oxygen

What neurotransmitter is released by the postganglionic axon

norepinephrine (adrenaline)

Where do cranial nerves and fibers (PNS) arise from

bottom portion of spinal cord

the parasympathetic division gives us responses associated with _____

a relaxed state; our rest and digest system

what neurotransmitter is used by the parasympathetic division

acetylcholine

what cells form myelin in the PNS

Schwann cells; they contain myelin in their membranes

What decides which axons have a myelin sheath and which don’t

length

long axons usually have a sheath, short axons don’t

What happens in Multiple Sclerosis

myelin breaks down (neurons can’t transmit info)

What does myelin help with in PNS injury

nerve regeneration within the PNS (sheath serves as passageway for new fiber growth)

What is a nerve impulse

an electrochemical signal (conveys info in the NS)

What is resting potential

the potential energy (voltage) of a neuron at rest

Why does the resting potential exist

because the plasma membrane is polarized; positive charge outside cell, negative charge inside

What maintains resting potential

sodium potassium pump (NA out, K in neuron)

Nerve signals are also called ______ and occur in ____

action potentials

axons

What is a stimulus to the neuron

a change that activates the neuron

What is the neuron threshold

minimum voltage (-55 mV) that must be reached in order for an action potential to occur

What does the neuron do to convey a stronger signal (instead of changing action potential size)

It causes more action potential/ “fires more”

What happens during depolarization/ AP begins

Na+ channels open, Na+ rushes into cell

inside of cell becomes positive

What happens in repolarization / after depolarization

Na+ channels close, K+ channels open and K+ flows out of cell

inside cell becomes negative again → AP complete

How long is the entire process of depolarization to repolarization

only 3-4 milliseconds to complete

How much is an unmyelinated axon AP slowed

slowed by 1 ms because each axon section must be stimulated

What is saltatory conduction

AP’s jumping from node to node along the myelinated axon

faster than unmyelinated

what is the refractory period and why is it important

the period of time immediately after an AP when the axon is unable to conduct another AP

ensures one-way direction of signal

what are axon terminals and what structures are they near

the fine endings of axons

each terminal is close to a dendrite or cell body of another neuron

What is a synaptic cleft

small gap separating sending neuron from receiving neuron

What do neurotransmitters do for AP’s? Where are these NT’s stored?

transmit AP’s across synapse (junction between neurons)

stored in synaptic vesicles in axon terminals

What happens when an AP reaches the axon terminal

calcium ions enter the terminal and stimulate synaptic vesicles to merge with sending membrane

NT released into cleft and diffuses across to receiving membrane and bind to receptor proteins

What causes an excitatory response from the receiving neuron

if neurotransmitter causes sodium gates to open

what causes an inhibitory response from the receiving neuron

if neurotransmitter causes potassium gates to open

What is integration

summing up of multiple incoming excitatory and inhibitory signals

What happens when there are more excitatory signals vs inhibitory signals in integration

excitatory: it’s axon will transmit a signal

inhibitory: signals may prohibit axon from reaching threshold

After a NT has initiated a response it is removed from the synaptic cleft, why must it be removed?

to prevent continuous stimulation of receiving membranes

What 2 ways can NT’s be removed from the cleft?

• Some synapses have enzymes that will inactivate the NT

• Other synapses have the sending membrane reabsorb the NT

Where are ACh and NE located in the PNS

neuromuscular junctions

What are the roles of ACh and NE in the PNS

ACh: excites skeletal muscle but inhibits cardiac muscle

NE: excites smooth muscle

What does a sensory receptor do?

Conducts sensory transduction:

converts signals from environment (stimuli) into nerve impulses

what are exteroceptors

sensory receptors that detect stimuli from outside the body (taste, smell, vision, hearing etc and send to CNS)

what are interoceptors

sensory receptors that receive stimuli from inside the body (homeostasis involved)

List the 4 sensory (exteroceptor) receptor categories (based on what stimulus is detected)

Chemoreceptors, photoreceptors, mechanoreceptors, thermoreceptors

What do chemoreceptors respond to?

chemical substances (taste, smell, blood pH)

• ex. nociceptors (pain receptors)

What do photoreceptors respond to?

light

What are mechanoreceptors stimulated by?

by mechanical forces (hearing, balance, touch, blood pressure)

What are thermoreceptors stimulated by?

changes in temperature; regulate body temperature

(in hypothalamus and skin)

define sensation and where it occurs

the conscious perception of stimuli

cerebral cortex

The sensation that we feel depends on what?

Which part of the brain receives the nerve signals

What happens before sensory receptors initiate nerve signals?

integration

What is sensory adaptation

a type of integration involving a decrease in response to a stimulus over time (sensory receptors send fewer impulses to the brain)

What are somatic senses associated with

skin, muscles, joints, viscera

What are the three types of somatic receptors (based on where receptors are)

proprioceptors, cutaneous receptors, and pain receptors

Where do all somatic receptors send nerve impulses

to primary somatosensory area of cerebral cortex via the spinal cord

What do free nerve endings detect

stimuli we perceive as pain and itching

What are proprioceptors/ what do they detect?

a type of mechanoreceptor involved muscle tone, equilibrium, posture

What are muscle spindles

a proprioceptor embedded in muscle fibers

Detect stretch → cause contraction

What are Golgi tendon organs?

a proprioceptor in tendoms

Detect tension → cause relaxation

What reflex involves proprioceptors(muscle spindles)?

knee jerk reflex → maintains posture

What do cutaneous receptors detect?

touch, pressure, pain, temperature

Meissner corpuscles, Krause end bulbs; all cutaneous receptors that detect….

fine touch in fingertips, palms, lips, tongue etc.

Where are Merkel disks (cutaneous receptors) found?

where epidermis meets the dermis

Root hair plexus (cutaneous receptor) detects….

hair touch

Where are the following cutaneous pressure sensitive receptors located: Pacinian corpuscles, Ruffini endings?

Pacinian: onion shaped in dermis

Ruffini: in connective tissue

What are thermoreceptors (cutaneous receptor type)

free nerve endings in the epidermis (some respond to cold, some to warm)

What happens leading up to binding of pain receptors (chemoreceptor type)?

tissue is damaged → release prostaglandin chemical → bind to nociceptors (pain receptor)

How does aspirin/ibuprofen reduce pain

by inhibiting enzymes that make prostaglandins (the pain receptor binding chemical)

What is referred pain

stimulation of nociceptors in internal organs is felt as pain in the skin

• eg. pain from heart felt in left arm

what are the three layers of the eye (describe them)

• sclera: outer white layer, fibrous (cornea inside is clear)

• choroid: middle layer, dark pigment absorbs light

• retina

what does the choroid form?

choroid → becomes iris → thickens and then forms ciliary body

iris function

regulates pupil size (hole where light enters eye)

ciliary body function

controls shape of lens for focusing

what attaches the lens to the ciliary body

suspensory ligaments

what are the two compartments of the eye made by

anterior:in front of lens, filled with clear liquid- aqueous humour

posterior: behind the lens, vitreous humor holds retina in place

When causes glaucoma and what does this result in

when the drainage ducts are blocked and the aqueous humor in the anterior compartment builds up

pressure compresses the arteries that serve retina → loss of vision

in which compartment is the third layer of the eye

the posterior compartment

What are the photoreceptors called that are within the retina layer

rods: light sensitive, no colour

cones: need bright light, detect colour

_____ is packed with cone cells

fovea centralis; when we look directly at an object it focuses on this

______ is made of sensory fibres from the retina

optic nerve; it takes nerve signals to the visual cortex in the occipital lobe

what do the cornea, lens and humor all do together

focus images on the retina (this image is inverted and reversed left to right on the retina)

when does the ciliary muscle contract vs relax, and when is lens flat vs round

relaxed muscle, flat lens: viewing a distant object

contract muscle, round lens: viewing a near object

what is eye strain, what age is this common

Fatigue from close work (contraction of ciliary muscle)

ages 40+ because lens loses elasticity

what segments do both rods and cones have

outer segment joined to an inner segment by a short stalk

where are pigment molecules located?

outer membrane of rods and cones, in the membrane of disks

where are synaptic vesicles of rods and cones located?

at synaptic endings of the inner segment of rods and cones

what is rhodopsin?

the visual pigment in rods

what happens to rhodopsin when a rod absorbs light

splits into opsin and retinal leading to a cascade of reactions → release of inhibitory NT’s

what provides us with peripheral vision

rods

what are the three types of cones?

B(blue), G(green), R(red)

combinations of cones are stimulated by in between shades of colour

what are the three layers of neurons within the retina

1. rod and cell cones (layer closest to choroid)

2. layer of bipolar cells (covers rods and cones)

3. ganglion cells (innermost layer, fibres = optic nerve)

what is the blind spot? how do we still have complete vision if we have blind spots?

where the optic nerve exits the eye

blind spot for right eye isn’t the same as blind spot for left eye so altogether we have complete vision

nerve impulses are carried by the optic nerves from the eyes to the ______

optic chiasma; theX shaped crossing over of optic nerve fibres

after exiting the optic chiasma, the optic nerve continues as ____ leading to ______

optic tracts

the thalamus

where does the thalamus direct nerve signals from the eye

the visual cortex in the occipital lobe

what structure is defective in colour blindness

one type of cone is defective or deficient in number (typically inability to see red and green)

what population is more susceptible to colour blindness

Males who have only one X chromosome (since gene is on the X chromosome)

• affects 5-8% male population

What is 20/20 vision

you can see clearly at 20 feet what should normally be seen from that distance (good vision, not perfect)

what is nearsightedness and what causes it

can see close, cannot see far

eye is elongated; distant objects are brought into focus too far in front of retina

what solution is there for nearsightedness

wearing concave lenses (they spread light rays)