Topic 14 Flashcards
The nervous system
Coordinates and regulates body functions
. Contains neurones through which electrical impulses travel along
The nervous system: Mammalian nervous system
Central nervous system (CNS): brain and spinal chord
Peripheral nervous system (PNS): neurones outside CNS
The nervous system: reflex actions
Rapid, automatic responses to stimuli that don’t involve the conscious part of the brain -> passage of nerve impulses in reflex action is called reflex arc
The nervous system: sequence of events in a reflex arc
Stimulus -> receptor -> coordinator -> effector -> response
1. Stimulus detected by receptors
2. Impulses sent along sensory neuron to CNS
3. Impulses cross synapse between sensory and relay neurone -> impulses continue along relay neuron
4. Impulses cross synapse between relay and motor neuron -> impulses continue along motor neuron
5. Then impulses reach effector -> If it’s a muscle it contracts and if it’s a gland it secretes a hormone
Types of neurons
. Sensory neurones
. Relay neurones
. Motor neurones
Synapses
Junction between two neurones
- Structure:
. Vesicles containing neurotransmitters
. Synaptic gap
. Receptor proteins
Nerve impulse passing through synapse:
- Impulse stimulates release of a neurotransmitter molecules from vesicles into synaptic gap
- Neurotransmitter molecules diffuse across gap
- Neurotransmitter molecules bind with receptor proteins ( on 1 side so impulses have one direction) on next neuron
- Impulse is then stimulated in next neurone
Sense organs
Sense organ: group of receptor cells responding to specific stimuli -> light, sound, touch, temperatures and chemicals
Structures of eye
Cornea: refelcts light
Iris: controls how much light enters pupil
Lens: focuses light onto retina
Retina: contains light receptors -> some sensitive to light of different colours
Optic nerve: carries impulses to brain
Types of receptors in eyes: Rods
. Found in peripheral parts of retina
. Very light sensitive -> work well in dim light
. 1 type of rod gives info in black and white -> not colour vision
Types of receptors in eyes: cones
. Found packed together in fovea
. Less light sensitive -> work best in bright light
. 3 types of cones give info in different colours -> colour vision
The eyes: pupil reflex
Antagonisitic action of circular and radial muscles in iris
. To make pupil wider: radial muscles contract and circular mucles relax -> increases light that enters eye
. To make pupil smaller: circular muscles contract and radial muscles relax -> decreases light that enters eye
The eyes: accomodation -> near objects
Eye focuses light on retina by changing the shape of the lens
- Near objects:
. Ciliary muscles contract -> slackens suspensory ligaments
. Lens becomes fat (more curved)
. Increases amount by which light is refracted
The eyes: accomodation -> distant objects
- Distant objects:
. Ciliary muscles relax -> suspensory ligaments pull tight
. Lens goes thin (less curved)
. Decreases amount by which light is refracted
Hormones
A chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
. Endocrine glands: produce and secrete hormones
Hormones: endocrine glands
. Adrenal glands: secrete adrenaline
. Ovaries: secrete oestrogen
. Testes: secrete testosterone
. Pancreas: secretes insulin and glucagon
Hormones: adrenaline
Hormone secreted in ‘fight or flight’ situations
- Effects:
. Increased breathing rate
. Increased pupil diameter
. Causes heart muscle to contract more frequently and with more force -> heart rate increases
. Causes liver to breakdown it’s glycogen stores to release glucose -> blood glucose level increases
Hormones VS nerve impulses: Hormone
. Slower message
. Act for long time
Hormones VS nerve impulses: nerve impulses
. Very fast message
. Act for very short time
Homeostasis
Maintenace of a constant internal environment
. Homeostatic control: kept using negative feedback systems -> body receptors detect a condition has gone above/below its normal level + trigger a response to bring level back to its set point again
Internal body temperature -> mechanisms to reduce body temperature: hairs lie flat
Less air is trapped -> skin less insulated + heat lost easily
Internal body temperature -> mechanisms to reduce body temperature: sweating
Water in sweat evaporates from skin surface taking heat from body
Internal body temperature -> mechanisms to reduce body temperature: vasolidation
Arterioles near skin surface dilate + more blood through capillaries near skin surface -> heat loss
Internal body temperatures -> mechanisms to increase body temperature: hairs stand up
Traps an insulating layer of air -> prevents heat loss
