Biology

ear can discriminate between different soundwaves because of different responsiveness of hair cells along the length of the cochlea.

base of the cochlea --> basilar membrae = narrow, thin and rigid --> high frequencies

apex of the cochlea --Y baislar membrane = wider and less rigid --> low frequency sounds.

depend on the number of neurones that are activated an the frequency of their impulses.

come form the vestibular apparatus in the inner ear.

The vestibular appartus consists of the semicircular canals, containing organs called cristae, and sacs called the saccule and utricle, containing organs called maculae.

The inner ear has three semicircular canals, each lying in a different plane at right angles to the other two. --> changes of movement (accleration / deccleration) in any direction can be detected.

Each canal is filed with fluid (endolymph)and has a small swelling (ampulla) containing a sense organ.

The sense organ called crista, has hair cells embedded in a gelatinous structure called a cupula. The cupula moves in response to movements of the endolymph canal, bending the cilia that project from the hair cells.

they produce generator potentials --> treshold level

two sacs in the vestibular aparatus contain sense organs called maculae , which are lined with hair cells sourrounded by a jelly-like fluid. Fine granules ove in response to changes in body positiion and bend the cilia on the hair cells. If the cilia bend in one direction, the frequency of nerve impulses increases, bending the cilia in the other direction decreases the frequency.

The information from the vestibular appartus is transmitted to several parts of the cnetral nervous system: spinal cord --> body position, cerebellum --> smooth coordinated movements, higher centres of the brain --> control of eye movements

nerve impulses

A resting neurone is so called because it does not convey a nerve immpulse, not because it is inactive. a resting neurone expends much eergy in maintaining a potenntial difference across its membrane.

measured: about - 70 milivolts.

During the resting potential, the inside of a neurone is negative relative to the outside because of an unequel distribution of charged ions.

On the outside, sodium ions Na+, chloride ions Cl- and calcium IOns Ca2+ are present in higher concentrations than inside the cell. By contras the inside of the cell has a higher concentration of potassium ions K+ and organic anions (negative ions).

This unequela distribution of ions results from a combination of active transport and diffusion of sodium and potassium ions across the cell membrane, and the inability of large organic anions to pass out of the cell. A sodium-potassium pump actively transports sodium ions out of the neurone and potassium ions in.

This wouldn't be enough. --> membrane is about 50 times more permeable to potassium ions than to sodium ions. potassium ions --> able to diffuse back out of the cell down their concentration gradient. sodium ions diffuse back ionto the cell only very slowly. --> negative electrical charge inside

the axon becomes depolarised (the inside becomes temporarily less negative). If the stimulus is strong enought (exceeds the threshold level) --> action potential occurrs.

--> complete change of the charge across the nerve cell:

• interior becomes positively charged relative to the outside
• +35 milivlts
• potential difference then back down, undershoots the resting potential and finally returns to it.

entire action potential --> 7 miliseconds

The return of the potential difference towards the resting potential.

the ability to respond appropritaley to stimuli, is one of the characteristic featers of life. Each organism has its own sepcific type of sensitivity that imporves its chances of survival.

In large multicellular animals such as mammals, stimuli are detected in sense organs.

Body part or cell that reacts to a stimulus in a particular way, or a cell substance in the body that produces an effect. p. ex. In a reflex the effector muscle acts before your brain is able to think.

and organs tat respond to sttimuli are called effectors.

The interconnections form circuits which enable us to control our muscles, think, remember and even sturd our own brains.

the nervous system and the endocrine system. Both involve cell signaling.

neurones, which convey information as nerve impulses (electrochemical signals)

a cell body, containing a nucles, and nerve fibres, long extensions that transmit nerve impulses rapidly from one part of the body to another.

axons

dendrons

small dendrons (dendrites) extending from the cell body

In mammals, sensory neurones carry messages from peripherial sense organs to a central nervous system (CNS) consisiting of the brain and spinal cord. The CNS acts as an integration centre and processes information from many sources.

Motor neurones convey instructions from the CNS to effector organs (mainly muscles and glands). can convey information rapidly and over considerable distances

These fast-conducting neurones are enclosed along most of their lengt by a thick insulating material called the mylein sheat.

The mylein sheat is produced by special supporting cells called Schwann cells. The sheath is essentially a series of cell membranes, each produced by a Schwann cell and wrapped many times around the axon.