Animal Physiology Final Exam

sensory neurons

Sensors detect external stimuli and internal conditions and transmit information along these

CNS

Integration takes place here, this includes the brain and a nerve cord

PNS

Bring information into and out of the CNS

Dendrites

Most neurons have these, highly branched extensions that receive signals from other neurons

Axon

Typically a much longer extension that transmits signals to other cells at synapses

Axon hillock

Axon joins the cell body here

Synapse

junction between an axon and another cell

Synaptic terminal

passes information across the synapse in the form of chemical messengers called neurotransmitters

depolarization

membrane potential becomes less negative

repolarization

membrane potential returns to resting value

hyperpolarization

membrane potential becomes more negative then resting value

resting potential

• concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell

• Many open K+ channels and fewer open Na+ channels

• negative at rest

graded potential

• Change in ion permeability causes change in membrane potential

• vary in magnitude depending on strength of stimulus

• more neurotransmitter → more ion channels open → larger magnitude of graded potential

Action Potentials

• triggered by net (combined) graded potential at axon hillock (trigger zone)

• do not degrade over time or distance

• travel long distances along membrane

• all or none

• must reach threshold potential to fire

1. voltage-gated Na+ channels open first (depolarization)

2. voltage-gated Na+ that opened begin closing

3. Voltage-gated Na+ channels mostly closed at top

4. K+ channels open more slowly (repolarization)

5. K+ channels close slowly, relative refractory period cause by open K+ channels

Spatial summation

Graded potentials from different sites influence the net change

Temporal summation

Graded potentials that occur at slightly different times influence net change

Absolute refractory period

A second action potential cannot be initiated. Result of temporary inactivation of the Na+ channels

Nodes of Ranvier

Gaps in the myelin sheath where voltage-gated ion channels are found, APs formed here. APS in myelinated axons jump between these in a process called saltatory conduction

electrical synapses

Electrical current flows from one neuron to another via gap junctions

chemical synapses

chemical neurotransmitter carries information across the synapse (synaptic cleft)

Neurotransmitter action

Inhibitory neurotransmitter

• cause hyperpolarization of membrane, make postsynaptic cell less likely to generate an AP

Excitatory neurotransmitter

• cause depolarization of membrane, make postsynaptic cell more likely to generate an AP

Voltage-Gates Ca2+ Channels

• concentrated around the axon terminal

• open at the same tie or instead of voltage-gated Na+ channels

• Ca2+ enters the cell, causing depolarization

• Ca2+ influx is slower and more sustained than Na+ influx

• slower maximal frequency of APs due to longer refractory period

Amount of Neurotransmitter Released

• Ca2+ is affected by AP frequency. More open Ca2+ channels = more Ca2+

• Factors that lower intracellular Ca2+ → binding with intracellular buffers and Ca2+ ATPases both lower Ca2+

• High AP frequency means more Ca2+ influx, more neurotransmitter in synapse, stronger response in post-synaptic cell

Acetylcholine

how it moves through the synapse

Striated muscle

• skeletal and cardiac muscle

• actin and myosin arranged in parallel

Smooth muscle

• actin and myosin are not arranged in any particular way

Vertebrate skeletal muscle

Skeletal muscle consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscle, each muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally.

Myofibril types

• thin filament: consists of two strands of actin and one strand of regulatory protein

• thick filament: staggered arrays of myosin molecules

Sarcomere

Filaments slide past each other longitudinally, producing more overlap between thin and thick filaments. For a muscle to contract, myosin-binding sites must be uncovered, when Ca2+ binds to a set of regulatory proteins called the troponin complex. Muscles contract when concentration of Ca2+ is high, stops when Ca2+ is low.

Cross bridge cycle

A skeletal muscle fiber contracts only when stimulated by a motor neuron. When a muscle is at rest, myosin-binding sites on the thin filament are blocked by ther regulatory protein tropomyosin

Role of S.R. and calcium in regulating contractions

• synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine

• acetylcholine depolarizes the muscle cell, causing it to produce an action potential

• AP travels to interior of muscle fiber along transverse (T) tubules

• AP along T-tubule causes the SR to release Ca2+

• Ca2+ binds to troponin complex on the thin filaments

• this binding exposes myosin-binding sites and allows the cross-bridge cycle to proceed

Graded contractions

Extent and strength of contraction can be voluntarily altered.

1. varying number of fibers that contract

2. varying rate at which fibers are stimulated

Recruitment of multiple motor neurons results in stronger contractions

Muscle twitch

Results from a single AP in a motor neuron. More rapidly delivered APs produce graded contraction by summation

Tetanus

Smooth and sustained contraction produced when motor neurons deliver a volley of action potentials

Oxidative muscles

Rely on aerobic respiration to generate ATP, many mitochondria, rich blood supply, much myoglobin. Binds oxygen more tightly than hemoglobin does.

Glycolytic muscles

Use glycolysis as primary source of ATP, less myoglobin, tire more easily

slow-twitch muscles

Type 1, contract more slowly, can contract more times before fatiguing, oxidative

fast-twitch muscles

type 2, contract more rapidly, can contract fewer times before fatiguing, glycolytic OR glycolytic and oxidative

muscle growth

Muscle size can be increased, number of muscle cells cannot be increased, number of actin and myosin filaments within a muscle cell can be increased

Satellite cells

Responsible for muscle growth and repair. Stressed muscles release IGF which stimulates satellite cell proliferation and differentiation

Myoglobin

Protein that binds oxygen more tightly than hemoglobin does

Fuels for muscles

• short- moderate length, high- intensity activity: glucose is main fuel, controlled by insulin and cortisol

• sustained high activity: glycogen depeted, triglycerides mobilized

Capillaries for O2 delivery to muscles

Rate of oxygen delivery depends upon capillary density, blood flow is determined by vascular tone and oxygen affinity of hemoglobin

Capillary tortuosity

Capillaries are not straight, O2 levels decline along length of capillary, region of muscle may be served by many capillaries that weave back and forth in areas that need more oxygen. Angiogenesis (synthesis of new blood vessels)

Metabolic transitions

For prolonged exercise, metabolic fuels must be mobilized for ATP production

Photoreception

ability to detect a small proportion of the electromagnetic spectrum from ultraviolet to near infrared

Photoreceptors

range from single light-sensitive cells to complex, image-forming eyes. Vertebrates and “higher” invertebrates have ciliary photoreceptors in their eyes.

ciliary photoreceptors

• have a single, highly folded cilium

• folds form disks that contain photopigments.

• photopigments are molecules that absorb energy from photons

vertebrate photoreceptors

• vertebrates have ciliary photoreceptors; rods (black and white) and cones (color)

• both have inner and outer segments (outer segments contain photopigments and inner segments form synapses with other cells)

Rods

• ciliary photoreceptor

• outer segment is rod shaped

• sensitive to very dim light

• one type of photopigment

Cones

• ciliary photoreceptor

• outer segment is cone shaped

• sensitive to brighter light

• up to three types of photopigment in mammals

Photopigments

2 parts

Chromophore

• derivative of vitamin A (ex: retinal), absorption of light converts bond from cis to trans

Opsin

• G protein-coupled receptor protein

• opsin structure determines photopigment characteristics (ex: wavelength of light absorbed)

Phototransduction

Steps in photoreception

• chromophore absorbs energy from photon

• chromophore changes shape from cis to trans

• activated chromophore dissociates from opsin “bleaching”

• opsin activates G-protein transduction pathway

• ion channels open or close

• change in membrane potential

Light vs. dark on rods and cones

• In the dark- rods and cones release the neurotransmitter glutamate into synapses with neurons called bipolar cells

• Bipolar cells are either hyperpolarized or depolarized in response to glutamate

• In the light- rods and cones hyperpolarize, chutting off glutamate

• the bipolar cells are then either hyperpolarized or depolarized

Other types of neurons that contribute to information processing in the retina

• transmit signals from bipolar cells to the brain; these signals travel along the optic nerves, which are made of ganglion cell axons

• horizontal cells and amacrine cells help integrate visual information before it is sent to the brain

• interaction among different cells results in lateral inhibition, a greater contrast in image

Flat sheet eyes

• weak sense of direction and good sense of intensity.

• Often in larval forms or as accessory eyes in adults

cup shaped eyes

• Retinal sheet is folded to form a narrow aperture

• discrimination of light direction and intensity

• light-dark contrast

• poor image formation (poor resolution)

vesicular eyes

• present in most vertebrates

• lens in the aperture improves clarity and intensity

• lens refracts light and focuses it onto a single point on the retina

• image formation, good resolution

convex eyes

• annelids, arthropods

• photoreceptors radiate outwards, convex retina

eyespots

• cells or regions of a cell that contain photosensitive pigment, protist Euglena

Stages of eye complexity in mollusks

• pigment spot- light, dark, limited direction ex: limpets

• pigment cup- light, dark, good direction ex: slit shell mollusk

• simple optic cup- light, dark, very good direction, very blurred, dark, small image ex: nautilus

• eye with primitive lens- light, dark, excellent direction, blurry image ex: murex

• complex eye- light, dark, excellent direction, very sharp, very sharp image ex: octopus

Cephalopod eye and retina

• photoreceptors are on the surface of the retina

• supporting cells are located between photoreceptor cells, no outer layers of cells associated with photoreceptors

• axons of photoreceptors form optic nerve

Structure of the vertebrate eye

• sclera- white of the eye

• cornea- transparent anterior layer

• retina- layer of photoreceptor cells plus pigmented epithelial cells

• choroid- pigmented layer behind retina

• tapetum- layer in the choroid of nocturnal animals that reflects light

• iris- two layers of pigmented smooth muscle

• pupil- opening in iris allows light into eye

• lens- focuses image on retina

• ciliary body- muscles that change lens shape

• aqueous humor- fluid in the anterior chamber

• vitreous humor- gelatinous mass in the posterior chamber

Fovea

• region in center of retina, overlying bipolar and ganglion cells are pushed to the side (so more direct light path)

• contains only cones, color vision, provides the sharpest images

• image is focused on the fovea

Brain processes the visual signal

• AP travels from retina to brain

• optic nerves→ optic chiasm → optic tract → lateral geniculate nucleus → visual cortex

binocular vision

• eyes have overlapping visual fields 

• combine and compare information from each eye to form a 3D image

• depth perception

• info from left field of view going to left brain, info from right field of view going to the right brain

optic chiasm

• optic nerves meet at the _____ near the cerebral cortex and cross, with information from the right visual field sent to the left hemisphere of the brain and vice versa

Color vision

• detecting different wavelengths of visible light

• requires photopigments with different light sensitivities

• most mammals see 2 colors (dichromatic)

• humans see 3 (trichromatic) or 4 (tetrachromatic) colors

• birds, fish, reptiles see 4 or 5 (pentachromatic) colors

Rods vs Cones

Rods

• convergence- many rods synapse with a single bipolar cell, many bipolar cells synapse with a single ganglion cell

• ganglion cells have large receptive field

• poor resolution (fuzzy image)

Cones

• each cone synapses with a single bipolar cell

• each bipolar cell connects to a single ganglion cell

• ganglion cell has small receptive field

• high resolution

on- center ganglion cells

• stimulated by light in center of receptive field

• inhibited by light in periphery of receptive field

off- center ganglion cells

• stimulated by dark in center of receptive field

• inhibited by dark in periphery of receptive field

signal processing in the retina

• on and off regions of the receptive field of ganglion cells improve contrast of light and dark

• photoreceptors in center and periphery inhibit each other by lateral inhibition

Lateral inhibition in the retina

• horizontal cells are primarily (maybe all) inhibitory, and act on photoreceptors

• bipolar cells can either be inhibited or excited by photoreceptors

• amacrine cells are primarily inhibitory, acting mainly on bipolar cells

nerve structure

bundles of myelinated and sometimes unmyelinated axons enclosed in several layers of connective tissue

Spinal nerves

• branch from spinal cord

• enter and exit between adjacent vertebrae

• named based on region of vertebral column from which they emerge

• mixed nerves

Long Term Potentiation (LTP)

• Form of learning, involves an increase in the strength of synaptic transmission

• involves 2 glutamate receptors

• if the postsynaptic neuron is heavily stimulated, the set of receptors present on the postsynaptic membranes changes

Habituation

• decline in response to a stimulus after repeated exposure

• allows animal to ignore unimportant stimuli and focus on novel stimuli

• caused by changes in the presynaptic axon terminal at the synapse with the motor neuron (inactivation of some voltage gated Ca2+ channels= lower neurotransmitter release)

Sensitization

• increase in the response to a gentle stimulus after exposure to a strong stimulus

• caused by changes in the presynaptic axon terminal

Involves a secondary circuit

• serotonin released by facilitating interneuron → binds to receptors → activation of G-proteins → inactivation of K+ channels → higher AP duration → Ca2+ influx → higher neurotransmitter release by sensory neuron

Serotonin

• Keeps voltage-gated K+ channels deactivated. Can’t repolarize or hyperpolarize, more likely to fire

Drugs and the brain’s reward system

• some drugs are addictive because they increase activity of the brain’s reward system. These include cocaine, amphetamine, heroin, alcohol, and tobacco

• Addiction is characterized by compulsive consumption and an inability to control intake.

• Addictive drugs enhance the activity of the dopamine pathway

• Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug

Statocysts

• organ of equilibrium in invertebrates

• hollow, fluid-filled cavities lined with mechanosensory neurons

• statocysts contain statoliths (dense particles of calcium carbonate, movement of statoliths stimulate mechanoreceptors)

Vertebrate hair cells

• mechanoreceptor for hearing and balance

• modified epithelial cells ( not neurons)

• cilia on apical surface (kinocilium is a true cilium, stereocilia is a microvilli). Tips of stereocilia are connected by proteins (tip links)

• mechanosensitive ion channels in stereocilia (movement of stereocilia → change in permeability)

• change in membrane potential

• change in release of neurotransmitter from hair cell

Neutral position- channels open and K+ flowing in, cell releasing some neurotransmitter. APs fire at intermediate frequency in afferent nueron

bent hard to right: all K+ channels open, more Ca2+, more APs in afferent neuron

bent hard to left: most K+ channels closed, some Ca2+, rare single AP

• operate opposite of other cells. External rich in K+, internal rich in Na+

Lateral line system

• most fish and aquatic amphibians have a lateral line system along both sides of their body.

• Contains mechanoreceptors with hair cells that detect and respond to water movement.

• Array of neuromasts within pits or tubes running along the side of the body

neuromast

• Hair cells and cupula (stereocilia embedded in gelatinous cap)

• detect movement of water

Sound wave traced through ear

• Stapes pushes sound wave through, goes all the way around to round window.

• Cochlear duct is where the readings of vibrations happen

• Sheet of afferent neurons coming off the cochlea makes up the auditory nerve

• Pinna acts as a funnel to collect more sound, middle ear bones increase the amplitude of vibrations from the tympanic membrane to the oval window

• vestibular and tympanic canal filled with fluid (high Na+, low K+, same as interstitial fluid)

• Cochlear duct (high K+, low Na+), contains hair cells. Has a tectorial membrane.

Tectorial membrane doesn’t touch bottom of vestibular canal. Hair cells are stuck to bottom of tectorial membrane, sits on basilar membrane (moves up and down when part underneath moves)- we sense that as sound.

Structure of mammalian middle ear

• Perilymph- fills vestibular and tympanic ducts. Similar to extracellular fluids (high K+ and low Na+)

• Endolymph- fills cochlear duct, different from extracellular fluid (high K+ and low Na+)

• Organ of corti- hair cells on basilar membrane, inner and outer rows of hair cells, sterocilia embedded in tectorial membrane in cochlear duct (filled with endolymph)

encoding sound frequency

Basilar membrane is stiff and narrow at the proximal end and flexible and wide at distal end.

• high frequency sound vibrates stiff end

• low frequency sound vibrates flexible end

Owl ears

Brain uses time lags and differences in sound intensity to detect location of sound.

• sound in right ear first (sound located to the right)

• sound louder in right ear (sound located to the right)

• rotation of head helps localize sound

Vestibular apparatus

• detects movements.

• 3 semi-circular canals (can hear in all 3 dimensions) with enlarged region at one end (ampulla)

• two sack-like swellings (utricle and saccule)

Macula

• present in utricle and saccule

• mineralized otoliths suspended in a gelatinous matrix

• stereocilia of hair cells embedded in matrix

• >100,000 hair cells

• detect linear acceleration and tilting of head

Cristae

Neuromasts (cristae) in ampullae of circular canals. They detect angular acceleration

Down-regulation

Target cells can alter receptor numbers. Target cell decreases number of receptors, often due to high concentration ligand (insulin resistance)

Heart’s role in pumping blood

Left side of heart pumps and receives only O2 rich blood, right side receives and pumps only O2 poor blood

Path of blood through the heart

Blood flows into right ventricle, is pumped to lungs to get O2, O2 rich blood from lungs enters heart at left atrium and is pumped through the aorta to the body tissues by the left ventricle. Blood returns to the heart through the superior vena cava and inferior vena cava, which flows into the right atrium to the right ventricle.

Aorta

Provides blood to the heart through the coronary arteries and moves blood from the left ventricle to the body tissues. Semilunar valves contorl blood flow to the aorta and the pulmonary artery

Stroke volume

Amount of blood pumped in a single contraction

Cardiac output

volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume

control of contraction

• vertebrate hearts are myogenic (cardiomyocytes produce spontaneous rhythmic depolarizations)

• Cardiomyocytes are electrically coupled via gap junction to ensure coordinated contractions