B6 - Reflexes, Stimuli, & the Nervous System
- Created by: Lilly_B
- Created on: 10-04-15 16:02
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- B6 - Reflexes, Stimuli, & the Nervous System
- Responding to change
- When a room gets hotter, you sweat more
- Stimulus = temperature increase
- Triggered response = Increased sweating
- When a room gets hotter, you sweat more
- Simple Reflex Actions
- Simple reflex actions happen quickly as they're involuntary (automatic)
- Simple animals rely on reflex actions for most of their behaviour so they always respond n the same way to a particular stimulus
- E.g. woodlice move away from light
- Reflex actions help animals to survive, including finding food & hiding from predators
- A human baby shows newborn reflexes, including:
- Grasping - tightly gripping a finger in the palm
- Sucking a ****** or finger in the mouth
- Stepping when a foot touches a flat surface
- Adults also show reflex actions, for example:
- The pupil reflex stops light damaging cells in the retina - in light, some muscles in the iris contract
- If someone hits your leg just below the knee, your thigh muscles contract & your leg straightens - the knee jerk reflex
- If you pick up something hot, you immediately drop it before it an burn & damage the skin (pain receptors)
- Responding to Stimuli
- Receptors: used to detect stimuli - these include:
- Single cells, such as pain sensor cells in the skin
- Cells in complex organs, for example, cells in the retina
- Processing centres to receive information & co-ordinate responses
- Effectors to respond to stimuli - these include:
- Muscle cells, which contract to move part of the body
- Glands, whose cells release chemical hormones
- When multicellular organisms evolve, their bodies develop complex nervous & hormonal communication systems
- Nerve impulses are electrical signals - they bring about fast, short - lived responses
- Hormones travel in the blood. They cause slower, longer-lasting responses, for example:
- The pancreas makes insulin to control blood sugar
- Oestrogen helps to control the female menstrual cycle
- Receptors: used to detect stimuli - these include:
- The Nervous System
- In the nervous system, neurons (nerve cells) link receptor cells to effector cells
- Neurons transmit electrical impulses when stimulated
- A neuron has an axon - a long extension of the cytoplasm surrounded by a cell membrane
- Some axons are surrounded by a fatty sheath - this insulates the neurons from nearby cell, so electrical signals can pass along it quickly
- In humans & other vertebrates, the central nervous system (CNS) is made up of the spinal cord & brain - coordinates an animals response to stimuli
- In a simple reflex, impulses move from one part of the nervous system to the next in a reflex arc
- The peripheral nervous system (PNS) links to the CNS to the rest of the body - its made up of sensory & motor nurons
- Responding to change
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