nervous system (chapter 3 and 4)

• neurons • basic structure and functional unit of nervous system • highly specialised cells, designed for rapid communication of messages in the body

cell body: - contains the nucleus - responsible for controlling the functioning of the cell - surrounding nucleus is cytoplasm and organelles dendrites: - extensions of the cytoplasm of cell body - highly branched structure that carry nerve impulses axon: - a long extension of the cytoplasm - carrying nerve impulses away from cell body - ends by dividing into axon terminals myelin sheath: - fatty material - the gaps between are called nodes of Ranvier - Schwann cells are the nodes of myelin - main functions include: insulating, protecting axon from damage and increasing the speech of impulses - in the central nervous system, myelin sheath is produced by oligodendrocytes

• a gap that’s between the axon terminals of one neurons and the dendrites of another neuron • impulses are carried across the synapse occurs by the movement of chemicals (neurotransmitters) • the synapse between a neuron and skeletal muscle is called a neuromuscular junction

sensory: - a.k.a afferent or receptor neurons - carry messages from receptors in the sense organs, or skin, to central nervous system motor: - a.k.a efferent or effector neurons - carry messages from central nervous system to effectors in the muscles and glands interneuron: - a.k.a relay, association or connector neurons - located in CNS - link between sensory and motor

multipolar: - one axon and multiple dendrites extending from cell body - can be motor neurons or interneurons bipolar: - one axon and one dendrite - sensory afferent (eye, ear and nose - specialised) pseudounipolar: - one axon extending from cell body, which then separates into 2 extensions. one extension connects to axon terminals and the other to dendrites. - cell body lies to the side of the main axon. - sensory (afferent) neuron

• a nerve impulse is a electrochemical change that travels along a nerve fibre • involving a change in electrical voltage brought about by chemicals (concentration of ions inside and outside of the cell membrane of a neuron)

• 2 types of electrical charges: (+) and (-) • like charges repel, opposites attract • when opposite charges are separated, an electrical force tends to pull them together, which can be measured (in voltage by volts or millivolts - 1000mV = 1V) • when opposite charges come together energy is released • if a group of opposites are separated they have the potential (potential difference) to come together and release energy

• when come chemical substances dissolve in water they break up into charged particles, ions this happens in: • the extracellular fluid, which contains a high concentration of sodium chloride (NaCl) - Na+ and Cl- • the intracellular fluid, which contains less sodium chloride and more potassium ions (K+) and other negative ions from organic particles • the difference in the concentration of ions means there is potential inside and outside the cell, called membrane potential • the membrane potential of an unstimulated neuron is resting membrane potential, is measured at approx. -70mV (means that the potential inside the cell is 70mV less that outside) and due to the differences in distribution of K+ and Na+ = extra being more positively charged than intra. • there is 10x more Na+ extra than intra • cell membrane is only slightly permeable to sodium ions due to the limited number of sodium leakage (limiting the facilitated diffusion of sodium) • the concentration of K+ is 30x more intra than extra • membrane is highly permeable to K+ due to larger number of K+ leakage channels = more K+ than Na+ can diffuse • the concentration of chloride ions is > intra then extra • membrane is highly permeable to Cl- allowing their diffusion through protein channels

cannot diffuse through phospholipid bilayer directly, either through: • leakage channels: are always open • voltage-gated channels: only open once the nerve is stimulated

• thermoreceptors • osmoreceptors • chemoreceptors • mechanoreceptors • nocicereceptors

• are able to respond to heat or cold • thermoreceptors in the skin inform the brain of changes in the temperature outside the body • peripheral receptors in the skin and nerve endings are sensitive to either hot or cold temperatures (not both) • the core body temperature is monitored by thermoreceptors in the hypothalamus which can then regulate body temperature

• osmotic pressure is determined by the concentration of substances dissolved in the water of the blood plasma • the higher the concentration the higher osmotic pressure and vice versa • they are located in the hypothalamus and are highly sensitive • they stimulate the modulation of water levels in the blood (nephrons of the kidneys)

• are stimulated by particular chemicals • are present in the nose (to odours), mouth (sensitivity to taste) • internal chemoreceptors (in blood vessels) which are sensitive to body fluid composition, mainly the pH of the blood (H-), oxygen and carbon dioxide (regulation of breathing)

• touch receptors • are found in greater concentrations in the lips, fingertips and eyelids to ensure quick reflexes to protect oneself

• pain receptors • are found in the skin and do not adapt to ongoing stimulation • they are stimulated by damage to the tissue, poor blood flow or excessive stimulation from stimuli (heat/chemicals)

• it is a rapid, autonomic response to a change in the external or internal environment • some reflexes involve the unconscious part of the brain (though most are coordinated by the spinal cord) • e.g. jerking hand back from touching hot objects, sneezing due to irritants in the nasal cavity

• a stimulus is required to trigger a reflex • it is involuntary (occurs without conscious thought) • provides a rapid response • response is stereotyped (same every time)

• a stimulus ( pointless of pin) • a receptor (nocicereceptors in skin create a nerve impulse in a sensory neuron) • a sensory neuron (passes impulse to spinal cord) • a synapse (impulse may pass straight to motor neuron or though a relay neuron) • a motor neuron (carries impulse from spinal cord to a muscle - effector) • an effector (the muscle is stimulated to contract) • the response (jerking hand away from pin)

nervous: - responds more rapidly due to rapid travelling of impulse along nerve fibres (responds in milliseconds) - when stimulus ceases it stops generation of nerve impulses and the response - response lasts for short period of time - nervous messages are an electrochemical change that travels along the membrane of a neuron - impulses travel along a nerve fibre to a specific part of the body and often influence just one receptor endocrine: - responds slower as hormones are transported in the bloodstream (response can vary between a few seconds or days) - when stimulus ceases it continues (due to hormones being slower acting) response can lasts a considerable amount of time (years even) - endocrine messages are transported via bloodstream - hormones travel to all parts of the body and can often effect a number of organs similarities: - some substances can effect both hormones and neurotransmitters, e.g. noradrenaline, adh and dopamine - some hormones (oxytocin and adrenaline) are secreted by neurons into the extracellular fluid - some hormones and neurotransmitters have the same effect on the same target cells (e.g. noradrenaline and glucagon both act on the liver cells to cause glycogen to be broken down into glucose)

brain and spinal cord

made up of all the nerves, receptors etc.

bone: - made up of the cranium, which is the part of the skull that houses and protects the brain. - while the spinal cord is protected by the vertebral canal (an opening in the vertebrae) - these bones provide a strong, rigid structure for the protection of the CNS membranes (meninges): - are layers of connective tissue forming membranes - outer layer = dura mater, is tough and fibrous - middle layer = arachnoid mater, a loose mesh of fibres - inner layer = pia mater, which is more delicate containing blood vessels. cerebrospinal fluid: - occupies the space between the middle and inner layers of the meninges - it circulates through the cavities in the brain and through the vertebral canal - is a clear, watery fluid • 3 main functions: protection (a shock absorber cushioning any blows) support (suspension of the brain) transport (circulates around CNS and deposits and nutrients and carries away any wastes.

• cerebrum/cerebral cortex • corpus callosum • cerebellum • hypothalamus • medulla oblongata • spinal cord

higher-order functions such as thinking, reasoning, memory, learning and conscious awareness off surrounding