Nervous System Chapter 4: Spinal Cord

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Questions and Answers

What is the approximate length of the spinal cord?

90cm

45cm (correct)

30cm

60cm

What is the function of the vertebral column in relation to the spinal cord?

It generates nerve impulses

It provides structural support to the spinal cord

It protects the spinal cord (correct)

It insulates the spinal cord

Which type of reflex involves the output transmitted by motor neurons to skeletal muscles?

Conditioned reflex

Autonomic reflex

Innate reflex

Somatic reflex (correct)

How many pairs of cervical nerves are there?

8 pairs Signup and view all the answers

What is the term for the reflexes that result from learning and are processed by higher brain levels?

Conditioned reflexes Signup and view all the answers

What is the region of the spinal cord that contains the cell bodies of interneurons?

Dorsal horn Signup and view all the answers

What is the significance of the differential growth between the vertebral column and spinal cord?

It results in spinal nerves descending before emerging from the vertebral column Signup and view all the answers

Which type of reflex has only one synapse in the reflex arc?

Monosynaptic reflex Signup and view all the answers

What is the purpose of the central canal?

To contain cerebrospinal fluid Signup and view all the answers

What is the function of the brainstem in cranial reflexes?

It subconsciously integrates cranial reflexes Signup and view all the answers

What is a common pathway shared by inputs from the heart and the left upper extremity?

Afferent pathways Signup and view all the answers

Which reflex is an example of an innate reflex?

Withdrawal reflex Signup and view all the answers

What is the shape of the grey matter in the spinal cord?

Inner butterfly-shaped Signup and view all the answers

What is the term for the reflexes that are built-in, unlearned responses?

Innate reflexes Signup and view all the answers

Why might inputs from the heart be interrupted?

Because they have to compete with inputs from the left arm Signup and view all the answers

At what level of the vertebral column does the spinal cord extend?

L1-L2 vertebra level Signup and view all the answers

What is the primary function of the spinal cord in reflexes?

To integrate reflex activity between afferent input and efferent output Signup and view all the answers

Which reflex is an example of a polysynaptic reflex?

Most reflexes in the human body Signup and view all the answers

What is the function of the hypothalamus in cranial reflexes?

It subconsciously integrates cranial reflexes Signup and view all the answers

What is the role of the integrating center in the reflex arc?

To process all information available and make a decision about the response Signup and view all the answers

What is the example of a spinal reflex mentioned in the text?

The withdrawal reflex Signup and view all the answers

What is the function of the efferent pathway in the reflex arc?

To transmit instructions from the integrating center to the effector organ Signup and view all the answers

What is the definition of a reflex?

Any response that occurs automatically without conscious effort Signup and view all the answers

Where are spinal reflexes integrated?

In the spinal cord Signup and view all the answers

How many pairs of spinal nerves are there?

31 Signup and view all the answers

What is the function of afferent fibers?

Carry incoming signals from peripheral receptors Signup and view all the answers

What is the term for a specific region of body surface supplied by a particular spinal nerve?

Dermatome Signup and view all the answers

Where do efferent fibers originate from?

Grey matter of spinal cord Signup and view all the answers

What happens when there is an injury to the spinal cord?

There are sensory and/or motor deficits Signup and view all the answers

What is referred pain?

Pain originating from an internal organ that is referred to a corresponding surface region Signup and view all the answers

What is the function of the ventral root?

Carry outgoing signals to muscles and glands Signup and view all the answers

What is the term for the nerve that emerges from the vertebral column and traverses between the spinal cord and a particular region of the body?

Spinal nerve Signup and view all the answers

What is the primary function of the stretch reflex?

To contract and counteract muscle stretch Signup and view all the answers

What is the characteristic of a monosynaptic reflex?

It has only one synapse between afferent and efferent neurons Signup and view all the answers

What is the role of the integrating center in a basic spinal reflex?

To link afferent input to efferent responses Signup and view all the answers

What is the purpose of reciprocal innervation?

To simultaneously stimulate an agonist muscle and inhibit an antagonist muscle Signup and view all the answers

What is the trigger for the withdrawal reflex?

Painful stimulus Signup and view all the answers

What is the role of the afferent neuron in the stretch reflex?

To originate at a stretch-detecting receptor in skeletal muscle Signup and view all the answers

What happens to the antagonist muscle in the withdrawal reflex?

It is inhibited Signup and view all the answers

What is the function of the inhibitory interneuron in the withdrawal reflex?

To inhibit an antagonist muscle Signup and view all the answers

Study Notes

Spinal Cord

Long, slender cylinder of nerve tissue, extends from brain stem, approximately 45cm long and 1-1.5cm wide
Vertebral canal: a space formed by the vertebral column, contains the spinal cord, and exits through a large hole in the base of the skull
Descends through the vertebral canal, enclosed by the protective vertebral column

Spinal Nerves

Emerge from the spinal cord through spaces between the bony, wing-like arches of adjacent vertebrae
Named according to the region of the vertebral column from which they emerge:
- Cervical nerves (neck): 8 pairs, C1-C8
- Thoracic nerves (chest): 12 pairs, T1-T12
- Lumbar nerves (abdominal): 5 pairs, L1-L5
- Sacral nerves (pelvic): 5 pairs, S1-S5
- Coccygeal nerves (tailbone): 1 pair

Differential Growth

During development, the vertebral column grows 25cm longer than the spinal cord
Spinal cord segments giving spinal nerves are not aligned with corresponding intervertebral spaces
Most spinal nerves descend before emerging from the vertebral column at their corresponding space
The spinal cord extends only to the L1-L2 vertebra level (waist level)

Spinal Cord Grey Matter

Centrally located, functionally organized
Forms an inner butterfly-shaped region surrounded by outer white matter
Consists of neuronal cell bodies, their dendrites, and glial cells
Central canal: lies in the center of the grey matter, filled with CSF
Each half of the grey matter is divided into:
- Dorsal (posterior) horn: contains cell bodies of interneurons, on which sensory neurons terminate

Spinal Nerves and Reflexes

Spinal nerves are part of the peripheral nervous system, consisting of 31 pairs of nerves
Each spinal nerve has dorsal and ventral roots at each level, joining to form a spinal nerve
Emerges from the vertebral column, traverses between the spinal cord and a particular region of the body
Enclosed by connective tissue, following the same pathway
Does not contain complete nerve cells, only axonal portions of many neurons
Progressively branches, forming a vast network of peripheral nerves supplying the tissues

Reflexes

Reflex: any response that occurs automatically without conscious effort
Spinal cord is responsible for integrating many innate reflexes
Strategically located between the brain and afferent and efferent fibers of the PNS
Enables the spinal cord to fulfill its two primary functions:
- Serving as a link for transmission between the brain and the rest of the body
- Integrating reflex activity between afferent input and efferent output without involving the brain

Reflex Arc

The neural pathway involved in accomplishing reflex activity
Includes five basic components:
- Sensory receptor: responds to stimulus, detects changes in the environment
- Afferent pathway: relies on the action potential produced by the receptor
- Integrating center: processes all information, makes a decision about the appropriate response
- Efferent pathway: transmits instructions from the integrating center to the effector organ
- Effector organ: muscle or gland that carries out the desired response

Reflex Categories

Depending on the CNS level at which the reflex is integrated:
- Spinal reflexes: integrated by the spinal cord, example: withdrawal reflex
- Cranial reflexes: subconsciously integrated by lower levels of the brain (brainstem or hypothalamus), example: pupillary constriction
Depending on whether the reflex is inborn or learned:
- Innate (simple/basic) reflexes: built-in, unlearned responses, integrated by the spinal cord and brain stem, examples: withdrawal reflex, micturition reflex, pupillary constriction
- Conditioned (acquired) reflexes: result of learning, processed by higher brain levels, examples: increased salivation on smelling food
Depending on which efferent division of the PNS and which effector organs are involved:
- Somatic reflex: output transmitted by motor neurons to skeletal muscles, example: withdrawal reflex
- Autonomic (visceral) reflex: output carried via ANS to smooth muscles, cardiac muscle, or glands, examples: micturition reflex, pupillary constriction reflex, salivary reflex, baroreceptor reflex

Reflex Examples

Stretch reflex: involves afferent neurons originating at stretch-detecting receptors in skeletal muscles, terminating on efferent neurons supplying the same skeletal muscles, causing contraction to counteract the stretch
Monosynaptic reflex: only one synapse in the reflex arc, between afferent and efferent neurons
Withdrawal reflex: initiated to withdraw from a painful stimulus, involves receptors stimulated enough to reach threshold, action potential generated in afferent neurons, and reciprocal innervation of agonist and antagonist muscles

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Description

This quiz covers the structure and function of the spinal cord, including its location in the vertebral canal, and the spinal nerves that emerge from it.