Animal responses Flashcards
What’s the role of the nervous system?
to carry out rapid and well-coordinated responses to external stimuli
components of the NS (PMAP)
CNS + PNS
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SENSORY + MOTOR
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SOMATIC + AUTONOMIC
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SYMP + PARASYMPATHETIC
what are the two divisions of the nervous system?
- peripheral nervous system
- central nervous system
What are the two divisions of the peripheral nervous system?
- sensory system
- motor system
what are the divisions of the motor system?
- somatic nervous system
- autonomic nervous system
what’s the CNS
- the central part of the NS composed of the brain and spinal cord
- the brain contains mainly unmyelinated neurones (grey matter)
- also present in spinal cord however, there’s also lots of myelinated neurones (white matter)
- spinal cord protected by the vertebral column.
define the PNS
- the sensory neurones (connecting sensory receptors to CNS)
- motor neurones (connecting CNS to effectors)
what’s the sensory nervous system?
- sensory neurones conduct ac pots from sensory receptors into the CNS
what’s the motor nervous system?
- conducts ac pots from CNS to effector
describe the autonomic nervous system
- part of the NS responsible for controlling the involuntary activities which are sunbconsciously controlled
- there are at least 2 neurones involved in the connection between the CNS and effector. Connected at small swellings called ganglia
- neurones are unmyelinated as rapid response not needed
- controls majority of the homeostatic responses
define the somatic nervous sytem
- Part of NS that controls voluntary activities under conscious control
- motor neurones are under conscious control
- one single neurone conducts ac pots from CNS to effectors under voluntary control (skeletal muscles)
- myelinated for rapid response
what are the divisions and functions of the autonomic nervous system?
- sympathetic system which prepares body for activity
- parasympathetic system which conserves energy
- they’re antagonistic
what are the four main parts of the brain?
- cerebrum
- cerebellum
- hypothalamus and pituitary gland
- medulla oblongata
function of cerebrum?
- largest part
- has two hemispheres connected by the corpus callosum
- outer layer is the cerebral cortex
- organises most of our highest thought processes like conscious thought, memory, intelligence
function of the cerebellum?
- coordinates movement and balance
- connected to the cerebrum by the pons
function of the hypothalamus and pituitary gland?
- organises homeostatic responses (thermoregulation and osmoregulation)
- pituitary gland releases hormones and stimulate other glands, controlled by the hypothalamus
function of the medulla oblongata?
- coordinates many autonomic responses (unconscious activities) like breathing and heart rate
- controls non-skeletal muscles
what’s a reflex action?
- a response to a stimulus that doesn’t involve the brain to coordinate movement
- nervous pathway is short so that reflex is rapid
why are reflexes important?
- used to get out of danger
- avoid damage to body part
- maintain balance
what’s a knee jerk reflex?
- a spinal reflex (passes through spinal cord) that straightens the leg when the quadricep is stretched to maintain balance
mechanism of knee jerk reflex
1) muscle spindles detect a stretch in the patellar tendon over the knee
2) sensory neurones conduct ac pot directly to a motor neurone in the spinal cord
3) motor neurone causes quadricep muscle to contract so the lower leg moves forward quickly, counteracting the change in length
why is the knee jerk reflex unusual
only consists of 2 neurones, absence of relay neurone means the pathway can’t be inhibited
what’s the blinking reflex?
a cranial reflex (passes through the brain) that causes temporary closure of the eyes from damage
mechanism of the blinking reflex
1) loud sounds, bright lights, foreign objects or movement is detected by sensory receptors in the cornea of the eye
2) sensory neurones conduct ac pots to the pons (in brain)
3) a motor neurone transmits ac pots to the eyelid muscles
4) eyelids contract to cause blinking, protecting the eye
what’s the mechanism corneal reflex?
- sensory neurone from the cornea conducts ac pot to relay neurone (in the pons) to motor neurone
- motor neurone conducts ac pot to the facial muscles and causes the eyelids to blink.
- sensory neurones also pass ac pots to myelinated neurones in the pons which carry it to the cerebral cortex
- this allows the reflex to be overridden by conscious control via inhibitory signals
the brain coordinates responses through output to the effectors. What are the outputs? ( what comes after motor)
- action potentials in the somatic nervous system
- ac pots in the sympathetic and parasympathetic parts of the autonomic nervous system
- release of hormones via the hypothalamus and pituitary glands
define ‘fight or flight’ response?
when an organism is threatened and it responds by preparing the body for action
how is the fight or flight response coordinated?
1) inputs feed into the in the cerebrum
2) the cerebrum conducts signals to the association centres
3) if a threat is recognised, the cerebrum stimulates the hypothalamus
4) hypothalamus increases activity in the sympathetic nervous system by stimulating the release of hormones from the anterior pituitary gland
How are prolonged responses achieved?
- by endocrine system
- sympathetic NS stimulates adrenal medulla to release adrenaline
what are tropic hormones?
hormones released by the anterior pituitary gland that stimulate the activity of endocrine glands
examples of hormones released by the hypothalamus
- corticotropin-releasing hormone (CRH)
- thyrotropin-releasing hormone (TRH)
effects of CRH (corticotropin-releasing hormone)
causes release of ACTH (adrenocorticotropic hormone) which stimulates adrenal glands to release glucocorticoids which increases glycogenolysis
effects of TRH (thyrotropin releasing hormone)
causes release of TSH (thyroid-stimulating hormone) which stimulates thyroid gland to release thyroxine which causes cells to increase their metabolic rate
What’s stroke volume?
volume of blood pumped per heart beat
what’s the role of the cardiovascular centre (in medulla oblongata)?
- alters the frequency of the waves of excitation from SAN
- nerves (part of the autonomic nervous system) from cardiovascular cenre supply the SAN.
What’s the accelerans nerve?
ac pots sent down this sympathetic nerve causes release of noradrenaline (neurotransmitter) at SAN which increases heart rate
What’s the vagus nerve?
nerve through which act pots pass through causing release of Ach which reduces heart rate
What’s the role of stretch receptors in muscles?
- detect movement of the limbs
- sends impulses to cardiovascular centre informing it that more oxygen may be needed
- this leads to an increase in heart rate ( accelerams nerve involved)
What are chemoreceptors ?
- receptors in the carotid arteries, aorta and brain that monitor pH of blood
- pH decreases (more acidic) during exercise, this is detected by chemoreceptors which send ac pots to CC which increases heart rate
- when exercise stops, conc of CO2 decreases which reduces activity of the accelerator pathway
What’s the role of stretch receptors in the walls of the carotid sinus?
- monitor blood pressure, if it becomes too high ac pots sent to CC leading to decrease in heart rate
how can heart rate be controlled artificially?
- artificial pacemaker which delivers electrical impulses to heart
What’s cardiac muscle?
muscle found in the heart walls
what’s involuntary muscle?
smooth muscle that contracts without conscious control
what’s skeletal muscle?
muscle under voluntary control
what do all muscles types have in common
- cells arranged to form fibres
- actin and myosin
structure and function of involuntary (smooth) muscle
- STRUCTURE
- spindle shaped cells
- uninucleate and bundles of actin and myosin
- arranged in longitudinal and circular layers
- not striated
- FUNCTION
- contacts slowly and regularly
- found in digestive system and blood vessels
- controlled by the autonomic nervous system
structure and function of cardiac muscle
- STRUCTURE
- striated but less than skeletal
- uninucleate
- FUNCTION
- myogenic
- cells form cross-bridges between fibres (helps ensure electrical stimulation spreads evenly over the walls of the chambers also ensures contraction is a squeezing action )
- cells joined by intercalated discs which allows diffusion of ions between cells and help in synchronised contraction
- doesn’t fatigue easily
- intermediate contraction speed
structure and function of skeletal muscle
- STRUCTURE
- cells form fibres
- striated (due to actin and myosin)
- multinucleate
- cylindrical cells
- FUNCTION
- arranged in antagonistic pairs: one contracts, other elongates
- fatigues quickly
- rapid contraction
- its contraction causes movement
- skeletal muscle occurs at joints in the skeleton
- controlled by somatic NS
what are myofibrils in skeletal muscle cells
- long cylindrical organelles which are divided into sarcomeres (basic functional unit of a fibre) which contain actin and myosin chains
- actin and myosin cause muscles to appear striated
- dArk bands = A bands
- lIghter bands = I bands
what’s the specialised endoplasmic reticulum called in skeletal muscle cells
sarcoplasmic reticulum
what’s the cytoplasm called in skeletal muscle cells
sarcoplasm which contains many mitochondria
what’s the sarcolemma in skeletal muscle cells
the membrane each fibre (cell) is surrounded by
bundles of myofibrils (which are muscle fibres) are surrounded by the…
sarcolemma
what’s the neuromuscular junction?
junction between nervous sytem and muscle
how is contraction of skeletal muscle stimulated?
- under voluntary control
- stimulated by somatic NS
1) ac pot arriving at end of axon opens Ca ion channels in membrane. Ca ions flood into the end of axon
2) vesicles of Ach move towards and fuse with the end membrane
3) Ach molecules diffuse across the gap and fuse with receptors in sarcolemma
4) this opens Na ion channels, allows them to enter muscle fibres causing depolarisation of sarcolemma
5) wave of depolarisation spreads along the sarcolemma and down t-tubules into muscle fibre
What’s a motor unit?
when many motor neurones connect to several muscle fibres and cause them all to contract providing stronger contraction
what are the two types of filament in myofibril ?
- thin filament which make up the light band, held together by Z line
- thick filaments which make up dark band
- both filaments surrounded by sarcoplasmic reticulum
what’s the H zone
- the middle of the dark band where thick and thin filaments don’t overlap
What’s the sarcomere
- distance between the two Z lines
composition of thin filaments
- filaments are actin
- each consists of two chains of actin subunits twisted around each other
- tropomyosin wrapped around the actin, toponin attached to tropomyosin
- each troponin complex consists of 3 polypeptides: one binds to actin, one to tropomyosin, and the other to Ca when it’s available
- at rest, troponin and tropomyosin cover binding sites to which thick filaments can bind
composition of thick filaments
- each filament consists of a bundle of myosin molecules.
- each myosin has two protruding heads which act as ATPase
- the heads are mobile and bind to actin when binding sites are exposed
the sliding filament hypothesis
- during contraction, light band and H zone get shorter
- so Z lines move closer together and sarcomere gets shorter.
- thick and thin filaments slide past one another
- myosin (thick filaments) remains the same
what are the main stages in muscle contraction
- stimulation
- attachment
- detachment
the mechanism of contraction
1) when muscle is stimulated, an ac pot passes along sarcolemma into the muscle fibre
2) ac pot is carried to the sarcoplasmic reticulum, which stores Ca ions, and causes the release of Ca ions into the sarcoplasm
3) Ca ions bind to troponin which alters its shape pulling the tropomyosin aside exposing binding sites on actin
4) myosin heads bind to actin, forming cross-bridges between the filaments
5) myosin heads move, pulling the actin filament past the myosin filament (power stroke), during this, ADP and Pi released from heads
6) new ATP molecule attaches to head, breaking cross-bridge, myosin heads detach from actin. ATP is hydrolysed releasing energy to make myosin head returns to original position
7) myosin heads can bind again further up actin filament
After contraction, Ca ions are actively transported back into the sarcoplasmic reticulum allowing muscle to relax
what’s bound to myosin heads when muscle is at rest
ADP
How is ATP supply maintained?
- aerobic respiration in mitochondria. Bohr effect helps to release more oxygen from Hb
- anaerobic respiration in sarcoplasm can produce a little more ATP. However causes build up of lactic acid (toxic) which causes fatigue
- creatine phosphate in sarcoplasm has phosphate groups which can be transferred to ADP creating ATP. Creatine phosphotransferase involved.
