Review 48-49 Ch 48 nervous system

1. Review 48-49 • Ch 48 nervous system • Nervous system consists of circuits of neurons & supporting cells • Sensory receptors-collect info about the world outside the body as well as inside

2. CNS=brain + spinal cord • PNS=nerves that communicate motor & sensory signal throughout the body • The evolution of the CNS is correlated w/bilateral symmetry

3. Motor output-conduction of signals from CNS to effector cells (muscle or gland cells that carry out responses) • Sensor-sensory input-integration-motor output-effector (page 1013) • An organism w/o integration centers couldn’t interpret stimuli

4. Sensory input LE 48-3 Sensor Integration Motor output Effector Central nervous system (CNS) Peripheral nervous system (PNS)

5. Neuron-functional unit of nervous system; composed of cell body w/nucleus + organelles; • dendrites are cell extension that receive incoming messages; • axons convey messages to other cells • an axon grows toward its target cells via cells along the growth path release signal molecules that either attract or repel the axon, & the interaction of CAMs on the growth cone & neighboring cells may provide tracks that guide axon growth

6. Many axons are covered by a myelin sheath (composed of Schwann cells or oligodendrocytes) • Synaptic terminals at the end of axons, relay signals from 1 neuron to another or other cells by neurotransmitters

7. Ganglia-cluster of nerve cells • Glia-supporting nerve cells, & they outnumber nerve cells in the body • *during development astrocytes cause tight junctions to be formed b/w cells that line the capillaries in the brain & spinal cord • This is the blood-brain barrier that stops the passage of most substances into the CNS • **this allows the extracellular chem environment of the CNS to be controlled

8. 3 kinds of glia cells: • astrocytes-provide support for neurons • Oligodendrocytes-form myelin sheaths in CNS • Schwann cell- myelin sheaths in PNS

9. Membrane potential describes the diff. in electrical charge across a cell membrane • The pm of a nerve cell at rest is resting potential (it exists b/c of diff. ion composition os x-cell & intracell fluids across PM) • Changes in the membrane potential of a neuron give rise to nerve impulses

10. A stimulus 1st affects membrane permeability to ions, & this is a graded potential w/a magnitude proportional to size of stimulus • Sodium-potassium pumps of neurons pumps Na+ out & K+ into the cell • ** (so inhibitory would not open Na+ channels)

11. Action potentials are an all-or-none depolarization of the membrane of the nerve cell. • It opens voltage-gated Na+ channels, & Na+ ions enter the cell bringing the membrane potential to a positive value. • Membrane potential is restored to its normal resting value by inactivation of Na+ channels & by opening voltage gated K+ channels, which ↑s K+ leaving the cell.

12. Saltatory conduction- jumping of the nerve impulses b/w nodes of Ranvier (not covered by sheath), it speeds up the conduction of the nerve impulse • The signal that is conducted from the axon of a presynaptic cell via an electrical or chemical synapse

13. Electrical synapses occur via gap junctions • In chemical synapses, ntm’s are released by the presynaptic membrane into the synaptic cleft. • They bind to receptors on the postsynaptic membrane & are then broken down by enzymes, or taken up by nearby cells

14. Direct synaptic transmission • The ntm binds directly to the ion channel causing it to open • Expiatory postsynaptic potential (EPSP) is the electrical charge caused by the binding of the ntm to its receptor on the postsynaptic membrane • Inhibitory postsynaptic potential (IPSP) is the voltage charge associated w/chemical signaling at an inhibitory synapse

15. Indirect synaptic transmission • Ntm binds to receptor that is not part of the ion channel causing a signal transduction pathway • Acetylcholine is a very common nt, it can be inhibitory or excitory • Other common nt’s are; epinephrine, norepinephrine, dopamine & serotonin

16. The PNS consists of paired cranial & spinal nerves & assoc. ganglia. • The PNS • somatic nervous system (skeletal muscles) • autonomic nervous system (automatic visceral functions of smooth & cardiac muscle)

17. somatic nervous system • Carries signals to & from skeletal muscles in response to external stimuli • **can be conscious control

18. Autonomic nervous system • sympathetic division (secretes adrenaline & increases heart rate) :”Fight or flight” • parasymphathetic division has the opposite effect when activated • Enteric division neurons in digestive tract, pancreas, & gall bladder (controls secretions & peristalsis)

19. The vertebrate brain develops from 3 embryonic regions: • forebrain, • midbrain, • Hindbrain • Most expansive growth occurs in the part of the forebrain which becomes the cerebrum • The establishment & expression of emotions involves the frontal lobes & limbic system

20. Brainstem is made of medulla oblongata, pons, & midbrain • Brainstem- controls homeostatic functions (breathing, sensory & motor signals, & regulates sleep & arousal) • Cerebellum- coordinates motor, perceptual, & cognitive functions

21. thalamus- main center through which sensory & motor info passes to & from cerebrum. • Hypothalamus regulates homeostasis (basic survival behavior like feeding, fighting, fleeing, reproducing, & circadian rhythms)

22. Cerebrum- 2 hemispheres each has cerebral cortex over white matter & basal nuclei, which are impt in planning & learning mvmts

23. Each side of the cortex has 4 lobes; frontal, temporal, occipital, & parietal, which contain primary sensory areas & association areas • Bilateral symmetry & cephalization is associated w/evolution of the CNS • If you were writing an essay, the part of the brain that would be most active is the temporal & frontal lobes

24. medulla oblongata-homeostatic control & contains regulatory centers for the respiratory & circulatory systems • cerebellum-coordination of mvmt & balance & coordinates muscle actions • corpus callosum-communication b/w the left & right cerebral cortices • hypothalamus-regulation of tm, hunger, & thirst; produces hormones that are secreted by the pituitary gland

25. CH 49 Sensory & motor mechanisms • Sensations-are action potentials that reach the brain via sensory neurons • Perceptions-such as colors, smells, sounds, & tastes are constructions formed in the brain & don’t exist outside it • If a tree falls in the woods & no one is around to hear it does it make a sound?

26. We can differentiate taste & smell b/c the action potentials initiated by taste receptors are transmitted to a diff. part of the brain than those initiated by receptors for smell • Sensory adaptation- ↓ in responsiveness during continued stimulation • i.e. when your skin is itchy after putting on a shirt & the itching stops after a few minutes

27. Sensations & perceptions begin w/sensory reception (detection by sensory cells/sensory receptors)

28. Mechanoreceptors-stimulated by physical stimuli (pressure, touch, motion, sound) • Thermoreceptors-respond to heat & cold & maintain body Tm (Thermoreceptors send signals to the posterior hypothalamus) • Chemoreceptors-solute concentration, taste & smell • Electromagnetic receptors-visible light, electricity, magnetism • Pain receptors- excess heat, pressure, damaged tissue

29. Hearing • Mechanoreceptors involved w/hearing & equilibrium detect settling particles or moving fluid

30. 3 regions in mammal ear • Outer ear-external pinna & auditory canal (these collect sound & direct them to the tympanic membrane/eardrum which separates outer from middle ear) • Middle ear vibrations are conducted through 3 small bones (malleus, incus, & stapes) & through the oval window • Then vibrations are conducted to the inner ear, which has a maze of channels lined by membrane & containing fluid, all situated in bone

31. Inner ear contains cochlea (2-chambered organ involved in hearing) • Organ of Corti in the cochlea has receptors of the ear which are “hairs” that project into the cochlear duct

32. Smell & taste • Taste & smell are closely related in most animals • Taste buds are modified epithelia cells on different parts of the tongue & mouth • Sensillae-taste receptors found on the feet & mouth of insects

33. Smell & taste • Taste receptors are modified epithelial cells organized into taste buds • Depolarization in taste receptors causes the cells to release neurotransmitter onto a sensory neuron • There are 5 categories of taste perceptions assoc w/ taste receptors (sour, salty, bitter, sweet, umami) • Transduction in taste receptors occurs by several diff mechanisms

34. Sight • Compound eyes have up to several hundred light detectors called ommatidia, each w/own lens • Single lens eyes are found in vert & some invert • **vitamin A is needed for healthy eyes

35. Main parts of the vertebrate eye: • sclera: white outer layer, including cornea • choroid: pigmented layer • conjunctiva: covers outer surface of sclera • iris: regulates the pupil • retina: contains photoreceptors • lens: focuses light on the retina

36. Eyeball in single lens eyes has 2 outer layers, the sclera (white) & choroid • The front the sclera becomes cornea (allows light into eye & acts like fixed lens) • Pupil also in eyeball is the hole in center of iris & retina (has photoreceptor cells)

37. Aqueous humor fills anterior cavity of the eye, & vitreous humor fills posterior cavity • Retina has rods (light) & cones (color) • Rhodopsin-light absorbing pigment that triggers a signal transduction pathway that leads to sight • I can SEE@!!!

38. grasshoppers have compound eyes w/ multiple ommatidia • Other insects as well have this & so it is diff to catch them

39. Movement • Animal skeletons function in support, protection, & mvmt • Locomotion-mvmt from place to place

40. Hydrostatic skeleton-fluid held under pressure in a closed body compartment • **Animals that have a hydrostatic skeleton can elongate, those that don’t can’t • Exoskeletons-hard encasements on surface of an animal (grasshopper) • Endoskeleton-hard supporting elements buried in soft tissue of an animal

41. Skeletal muscle-attached to bones & is responsible for mvmt of bones • Skeletal muscle consists of long fibers, each of which is a single muscle cell • Each muscle fiber is a bundle of myofibrils, which in turn are composed of 2 kinds of myofilaments; thin & thick filaments

42. Rigor mortis occurs when an organism dies & the muscles remain in a contracted state for a short amount of time; this is b/c there is no ATP to break the bonds b/w thick & thin filaments

43. Tetanus- sustained muscle contraction due to a lack of relaxation b/w successive stimuli

44. Describe how homeostasis is maintained for neuron resting-membrane potential • Explain how the nervous system functions to produce a response such as jumping or turning towards a loud noise