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Questions and Answers
Which part of the central nervous system is responsible for balance and coordination?
Which part of the central nervous system is responsible for balance and coordination?
How many segments are present in the cervical region of the spinal cord?
How many segments are present in the cervical region of the spinal cord?
What type of nerve fibers enter the spinal cord through the posterior root?
What type of nerve fibers enter the spinal cord through the posterior root?
Which region of the spinal cord contains 5 segments?
Which region of the spinal cord contains 5 segments?
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Which cranial nerve is known to be purely sensory?
Which cranial nerve is known to be purely sensory?
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What type of motor fibers leave the spinal cord through the anterior root?
What type of motor fibers leave the spinal cord through the anterior root?
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Which part of the nervous system lies outside of bony cavities?
Which part of the nervous system lies outside of bony cavities?
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Reflex actions are described as what in the nervous system?
Reflex actions are described as what in the nervous system?
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What is the role of receptors in the reflex arc?
What is the role of receptors in the reflex arc?
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Which component of the reflex arc is responsible for carrying impulses from the receptor to the CNS?
Which component of the reflex arc is responsible for carrying impulses from the receptor to the CNS?
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Which type of reflex action involves the contraction of skeletal muscles?
Which type of reflex action involves the contraction of skeletal muscles?
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In the autonomic reflex arc, what divides the efferent neuron into two different neurons?
In the autonomic reflex arc, what divides the efferent neuron into two different neurons?
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What is the primary function of the effector organ in the reflex arc?
What is the primary function of the effector organ in the reflex arc?
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Which type of receptors are sensitive to mechanical stimuli?
Which type of receptors are sensitive to mechanical stimuli?
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What is the center in a somatic reflex arc primarily composed of?
What is the center in a somatic reflex arc primarily composed of?
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Which statement about the autonomic reflex arc is true?
Which statement about the autonomic reflex arc is true?
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What is the primary function of thermoreceptors?
What is the primary function of thermoreceptors?
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Which type of receptor adapts rapidly to constant stimuli?
Which type of receptor adapts rapidly to constant stimuli?
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Which property of receptors allows them to respond by generating receptor potentials?
Which property of receptors allows them to respond by generating receptor potentials?
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What type of sensation is NOT categorized under mechanosensory?
What type of sensation is NOT categorized under mechanosensory?
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Which areas of the somatosensory cortex are primarily involved in processing sensory information?
Which areas of the somatosensory cortex are primarily involved in processing sensory information?
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Which of the following is a type of sensory fiber responsible for transmitting somatic sensations?
Which of the following is a type of sensory fiber responsible for transmitting somatic sensations?
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What characterizes the somatic sensory area I (SSI) in the brain?
What characterizes the somatic sensory area I (SSI) in the brain?
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Which statement best describes the adaptation of receptors?
Which statement best describes the adaptation of receptors?
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Study Notes
Nervous System Division
- The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
Central Nervous System (CNS)
- The CNS is composed of the brain and spinal cord.
- The brain is located inside the skull and consists of:
- Two cerebral hemispheres
- Cerebellum
- Brainstem (midbrain, pons, medulla oblongata)
- Diencephalon (thalamus, hypothalamus, parts of the basal ganglia)
- The spinal cord is located inside the vertebral column and is divided into five regions (31 segments):
- Cervical region (8 segments)
- Thoracic region (12 segments)
- Lumbar region (5 segments)
- Sacral region (5 segments)
- Coccygeal region (1 segment)
Peripheral Nervous System (PNS)
- The PNS is located outside bony cavities and includes:
- Cranial nerves (12 pairs) which arise from the brain
- Spinal nerves (31 pairs) each arising from a segment of the spinal cord
- Nerve fibers running in the spinal nerves can be sensory (afferent) or motor (efferent).
- Sensory (afferent) nerves carry impulses towards the spinal cord and:
- Enter the spinal cord through the posterior root of the spinal nerve
- Their cell bodies are located in the posterior (dorsal) root ganglion
- Can be somatic afferent (from receptors in somatic structures like skin, skeletal muscles, joints) or autonomic afferent (from receptors in the walls of the viscera such as the stomach, intestine, lungs, and heart).
- Motor (efferent) nerves carry impulses away from the spinal cord:
- Leave the spinal cord through the anterior root of the spinal nerve
- Their cell bodies are located in either the anterior horn cell (AHC) for somatic (voluntary) motor or the lateral horn cell (LHC) for autonomic (involuntary) motor.
Cranial and Spinal Nerves
- Cranial nerves can be sensory, motor, or mixed.
- All spinal nerves are mixed nerves.
- Some cranial nerves are purely afferent (e.g., optic nerve), while others are purely efferent (e.g., hypoglossal nerve).
- Some cranial nerves are mixed, containing both afferent and efferent fibers (e.g., vagus nerve).
Reflex Action
- Reflex action is the functional unit of the nervous system.
- It is an involuntary action that occurs in response to a stimulus (e.g., reflex closure of the eyelids in response to a moving object or reflex secretion of gastric juice on seeing or smelling food).
- Reflex action is mediated by the reflex arc.
Reflex Arc
- The reflex arc is the pathway of reflex action, composed of:
- Receptor: Detects stimuli and informs the CNS.
- Afferent neuron: Carries impulses from the receptor to the CNS.
- Center: Located in the CNS (either anterior horn cell (AHC) or lateral horn cell (LHC))
- Efferent neuron: Carries impulses from the CNS to the effector organ
- Effector organ: Produces the response (can be skeletal muscle, a gland, smooth muscle, or cardiac muscle).
Reflex Arc Types (Based on the Effector Organ)
- Somatic reflex actions: Involve contraction of skeletal muscles (e.g., withdrawal reflex).
- Autonomic reflex actions: Regulate the activity of non-voluntary organs (e.g., contraction of cardiac muscle, smooth muscle, or secretion of glands).
Somatic vs Autonomic Reflex Arcs
- The receptor, afferent neuron, and the effector organ are the same for both types of reflex arcs.
- However, the center is different and the efferent neuron is divided into two neurons for autonomic reflex arcs.
Somatic Reflex Arc
- Center: Anterior horn cell (AHC)
- Efferent neuron: One neuron
- Effector: Skeletal muscle
Autonomic Reflex Arc
- Center: Lateral horn cell (LHC)
- Efferent neuron: Two neurons:
- Preganglionic fiber: Starts from the LHC and relays in the autonomic ganglia.
- Postganglionic fiber: Starts from the autonomic ganglia.
- Effector: Smooth muscle, cardiac muscle, and glands.
Receptors: Specialized Cells or Neurons
- Receptors are specialized cells or neurons that detect internal and external environmental changes (stimuli).
- They convert the energy of a stimulus into electrical signals (impulses) that are transmitted by afferent neurons to the CNS.
Receptor Properties
- Specificity: Each receptor is adapted to respond to a specific type of stimulus.
- Excitability: Receptors respond to stimuli by generating a receptor potential, potentially leading to an action potential.
- Adaptation: Receptors exhibit a decline in the magnitude of their receptor potential and the number of impulses emitted, even if the stimulus remains constant.
Receptor Adaptation Types
- Rapidly adapting receptors (phasic receptors): Adapt quickly to constant stimuli and discharge strongly only during changes in stimulus (ON/OFF).
- Moderately adapting receptors: Show gradual adaptation, suitable for detecting changes in stimulus over time (e.g., temperature, smell, taste receptors).
- Slowly adapting receptors (non-adapting receptors): Exhibit minimal adaptation and provide continuous information about persistent stimuli (e.g., pain receptors, muscle spindles, and baroreceptors).
Receptor Classification (Based on Stimulus Type)
- Mechanoreceptors: Detect pressure, vibration, touch, stretch.
- Thermoreceptors: Detect changes in temperature.
- Pain receptors (nociceptors): Detect pain.
- Electromagnetic receptors: Detect light, magnetic fields, and electrical fields.
- Chemoreceptors: Detect changes in chemical concentrations (e.g., taste, smell, blood oxygen levels).
Somatic Sensations
- Somatic sensations arise from the skin, skeletal muscles, joints, and tendons.
- They provide information about:
- Touch
- Pressure
- Vibration
- Temperature
- Pain
- Proprioception (position and movement of the body)
Mechanoreceptors: Touch and Proprioception
- Touch:
- Crude touch: Detects general contact.
- Fine touch: Detects precise contact.
- Stereognosis: Ability to identify objects by touch.
- Pressure: Detects the amount of force applied to the skin.
- Vibration sense: Detects rapid oscillations of the skin.
- Itch and tickling: Stimulated by specific receptors.
- Proprioception:
- Sense of position: Awareness of body parts in space.
- Sense of movement: Awareness of body part motion.
Transmission of Somatic Sensations
- Sensory Afferents:
- Carry impulses from the periphery to the CNS.
- Classified into types A, B, and C fibers based on their diameter and conduction velocity.
- First-order neuron: Sensory neuron carrying impulses from the receptor to the spinal cord.
Somatosensory Cortex
- Receives and processes sensory information from the entire body.
- Located in the parietal lobe, behind the central sulcus.
- Occupies Brodmann's areas 1, 2, 3, 5, 7, and 40.
- Divided into three main areas:
- Somatic sensory area I (SSI):
- Located in the postcentral gyrus (Brodmann's areas 1, 2, and 3).
- Receives sensory information from the opposite side of the body.
- Shows spatial orientation, meaning that different parts of the body are represented in specific regions of the cortex.
- Somatic sensory area II (SSII): Located near the SSI.
- Association sensory area: Involved in integrating sensory information from different areas.
- Somatic sensory area I (SSI):
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