nervous system (chapter 3 and 4)

Question 1

nerve cells

Answer 1

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

Question 2

structure of neurons

Answer 2

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

Question 3

synapse between neurons

Answer 3

• 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

Question 4

types of neurons (functional)

Answer 4

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

Question 5

types of neurons (structural)

Answer 5

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

Question 6

conduction of a nerve impulse

Answer 6

• 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)

Question 7

electrical change and potential difference

Answer 7

• 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

Question 8

potential difference across cell membrane

Answer 8

• 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

Question 9

movement of ions through membrane

Answer 9

cannot diffuse through phospholipid bilayer directly, either through:

• leakage channels: are always open
• voltage-gated channels: only open once the nerve is stimulated

Question 10

types of receptors

Answer 10

• thermoreceptors
• osmoreceptors
• chemoreceptors
• mechanoreceptors
• nocicereceptors

Question 11

thermoreceptors

Answer 11

• 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

Question 12

osmoreceptors

Answer 12

• 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)

Question 13

chemoreceptors

Answer 13

• 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)

Question 14

mechanoreceptors

Answer 14

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

Question 15

nocicereceptors

Answer 15

• 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)

Question 16

what is a reflex

Answer 16

• 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

Question 17

what are the main properties of a reflex

Answer 17

• 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)

Question 18

stages of a reflex arc

Answer 18

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

Question 19

comparison of hormonal and nervous coordination

Answer 19

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)

Question 20

composition of central nervous system

Answer 20

brain and spinal cord

Question 21

composition of peripheral nervous system

Answer 21

made up of all the nerves, receptors etc.

Question 22

protection of the central nervous system

Answer 22

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.

Question 23

components of the brain

Answer 23

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

Question 24

cerebrum/cerebral cortex function

Answer 24

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

Question 25

corpus callosum function

Answer 25

a wide band of nerve fibres that cross from one cerebral hemisphere to the other, allowing communication between them

Question 26

cerebellum function

Answer 26

(consciously) controls posture, balance and fine coordination of voluntary muscle movement. it receives information from inner ear (posture and balance) and stretch receptors in skeletal muscles, thought doesn't originate there so movement is possible without it, but not refined

Question 27

hypothalamus function

Answer 27

maintains homeostasis, such as the regulation of autonomic nervous system (heart rate, diameter of pupil, secretion of digestive fluid), body temperature, appetite, concentration of urinary bladder, emotion and secretion of hormones

Question 28

medulla oblongata function

Answer 28

contains the cardiac centre (regulation of rate and force of heartbeat), respiratory centres (rate and depth of breath) and the vasomotor centre (regulates diameter of blood vessels) also controls other reflexes like sneezing, vomiting, swallowing etc. is under the influence of hypothalamus

Question 29

spinal cord function

Answer 29

provides a pathway for communication between muscles and glands and the brain; integration of autonomic, protective reflexes.

Question 30

types of nerves

Answer 30

cranial nerves: - 12 pairs of nerves - include optic and auditory nerves from the brain - most are mixed nerves, contain fibres that carry impulses to and from the brain - the ones that carry to brain = sensory, the ones that carry away from brain = motor spinal nerves: - 31 pairs of nerves - are mixed (contain both sensory and motor) - the ventral root contains the motor neuron - the dorsal root contains the sensory neuron

Question 31

division of peripheral nervous system

Answer 31

afferent division: - a.k.a sensory - has fibres that carry impulses into the cns by sensory neurons from receptors in the skin and around the muscles and joints - divided into: somatic sensory neurons: carry impulses from skin and muscles visceral sensory neurons: carry impulses from internal organs efferent division: - a.k.a motor - has fibres that carry impulses away from cns - divided into: somatic division: which takes impulses from cns to to skeletal muscles autonomic division: carries impulses to heart muscles, involuntary muscles and glands, divided into: - sympathetic - parasympathetic