14.3 - A Reflex Arc Flashcards
What are the two main divisions of the nervous system?
1) central nervous system (CNS): which is the brain and spinal cord
2) peripheral nervous system (PNS): which is made up of pairs of nerves originating from the brain or spinal cord.
How is the peripheral nervous system (PNS) divided?
- The PNS is divided into sensory neurons, which carry impulses from receptors towards the CNS, and motor neurons, which carry impulses from the CNS to effectors.
What are the two subdivisions of the motor nervous system?
- The motor nervous system is subdivided into:
1) the voluntary nervous system: which controls body muscles under conscious control
2) the autonomic nervous system: which regulates involuntary functions involving glands, smooth muscle, and cardiac muscle.
Describe the structure and location of the spinal cord.
- The spinal cord is a column of nervous tissue that runs along the back, lying within the vertebral column for protection.
- Nerve pairs emerge at intervals along its length.
What is a reflex arc?
A reflex arc is the pathway of neurons involved in an automatic, involuntary response to a stimulus, such as withdrawing a hand from a hot object.
Why is a reflex arc often called a spinal reflex?
Because one of the neurons in the reflex pathway is located in the spinal cord, enabling a quick, direct response without initial brain involvement.
What are the main stages of a spinal reflex arc?
1) Stimulus - e.g., heat from a hot object.
2) Receptor - temperature receptors in the skin generate impulses in the sensory neuron.
3) Sensory Neuron - transmits impulses to the spinal cord.
4) Coordinator - intermediate neuron in the spinal cord links sensory neuron to motor neuron.
5) Motor Neuron - carries impulses to the effector.
6) Effector - e.g., muscle in the upper arm, which contracts.
7) Response - pulling the hand away from the hot object.
Why are reflexes involuntary, and why is this advantageous?
- Reflexes are involuntary to avoid burdening the brain with simple decisions, allowing it to focus on complex tasks.
- This ensures a quick response and allows survival actions to be automatic.
How do reflex actions protect the body?
- Reflexes are protective as they are automatic, quick, and require no learning.
- This protects the body from immediate harm by initiating fast withdrawal from harmful stimuli.
Why are reflex arcs especially fast?
Reflex arcs are fast because they have short neuron pathways and involve few synapses, which are the slowest parts of the neuron pathway. There’s also no decision-making process, speeding up the response.
Why are synapses important in a reflex arc, and how do they affect the speed of response?
- Synapses allow communication between neurones through neurotransmitters, which ensures impulses continue along the pathway.
- However, they slow down the transmission slightly compared to direct electrical transmission within a neurone.
- Despite this delay, reflex pathways have very few synapses to keep the response as fast as possible, which is crucial for protection.
