The crossed extensor reflex is a withdrawal reflex. The reflex occurs when the flexors in the withdrawing limb contract and the extensors relax, while in the other limb, the opposite occurs. An example of this is when a person steps on a nail, the leg that is stepping on the nail pulls away, while the other leg takes the weight of the whole body. The crossed extensor reflex is contralateral, meaning the reflex occurs on the opposite side of the body from the stimulus.
To produce this reflex, branches of the afferent nerve fibers cross from the stimulated side of the body to the contralateral side of the spinal cord. There, they synapse with interneurons, which in turn, excite or inhibit alpha motor neurons to the muscles of the contralateral limb.
The withdrawal reflex nociceptive or flexor withdrawal reflex is a spinal reflex intended to protect the body from damaging stimuli. It is polysynaptic, and causes the stimulation of sensory, association, and motor neurons. When a person touches a hot object and withdraws his hand from it without thinking about it, the heat stimulates temperature and danger receptors in the skin, triggering a sensory impulse that travels to the central nervous system. The sensory neuron then synapses with interneurons that connect to motor neurons.
Some of these send motor impulses to the flexors to allow withdrawal. Some motor neurons send inhibitory impulses to the extensors so flexion is not inhibited—this is referred to as reciprocal innervation. Although this is a reflex, there are two interesting aspects to it:. Golgi tendon organ : The Golgi tendon organ, responsible for the Golgi tendon reflex, is diagrammed with its typical position in a muscle left , neuronal connections in spinal cord middle , and expanded schematic right.
The tendon organ is a stretch receptor that signals the amount of force on the muscle and protects the muscle from excessively heavy loads by causing the muscle to relax and drop the load.
Privacy Policy. Skip to main content. Peripheral Nervous System. Search for:. Components of a Reflex Arc A reflex arc defines the pathway by which a reflex travels—from the stimulus to sensory neuron to motor neuron to reflex muscle movement.
Learning Objectives Describe the components of a reflex arc. Key Takeaways Key Points Reflexes, or reflex actions, are involuntary, almost instantaneous movements in response to a specific stimulus.
Reflex arcs that contain only two neurons, a sensory and a motor neuron, are considered monosynaptic. Examples of monosynaptic reflex arcs in humans include the patellar reflex and the Achilles reflex. Most reflex arcs are polysynaptic, meaning multiple interneurons also called relay neurons interface between the sensory and motor neurons in the reflex pathway. Key Terms motor neuron : A neuron located in the central nervous system that projects its axon outside the CNS and directly or indirectly control muscles.
There are two types of reflex arcs: autonomic reflex arc affecting inner organs and somatic reflex arc affecting muscles. Cashdan, E. Hormones and competitive aggression in women. Aggressive Behavior, 29 2 , — Dabbs, J. Testosterone differences among college fraternities: Well-behaved vs. Personality and Individual Differences, 20 2 , — Gladue, B. Hormonal response to competition in human males.
Aggressive Behavior, 15 6 , — Macrae, C. Person perception across the menstrual cycle: Hormonal influences on social-cognitive functioning. Psychological Science, 13 6 , — Mazur, A. Testosterone and chess competition. Social Psychology Quarterly, 55 1 , 70— Tremblay, R. Testosterone, physical aggression, dominance, and physical development in early adolescence. International Journal of Behavioral Development, 22 4 , — Figure 4. The peripheral nervous system is both autonomic controlling internal activities of organs and glands and somatic controlling external actions of skin and muscles.
Skip to content Chapter 4. Brains, Bodies, and Behaviour. Explain how the electrical components of the nervous system and the chemical components of the endocrine system work together to influence behaviour. Key Takeaways The body uses both electrical and chemical systems to create homeostasis.
The ANS is further divided into the sympathetic activating and parasympathetic calming nervous systems.
These divisions are activated by glands and organs in the endocrine system. Specific nerves, including sensory neurons, motor neurons, and interneurons, each have specific functions. The spinal cord may bypass the brain by responding rapidly using reflexes.
The pituitary gland is a master gland, affecting many other glands. Hormones produced by the pituitary and adrenal glands regulate growth, stress, sexual functions, and chemical balance in the body. The adrenal glands produce epinephrine and norepinephrine, the hormones responsible for our reactions to stress. The sex hormones, testosterone, estrogen, and progesterone, play an important role in sex differences. Exercises and Critical Thinking Recall a time when you were threatened or stressed.
What physiological reactions did you experience in the situation, and what aspects of the endocrine system do you think created those reactions? Consider the emotions that you have experienced over the past several weeks.
What hormones do you think might have been involved in creating those emotions? Previous: 4. Skip to menu Skip to content Skip to footer. Site search Search. Site search Search Menu. Somatic nervous system. Autonomic nervous system Enteric nervous system Somatic nervous system. Emergency Phone:
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