Nervous System Lesson: Structure, Functions, Reflexes & Control
Lesson Overview
- What Is the Nervous System and Why Is It Vital to Human Survival?
- How Is the Nervous System Structurally and Functionally Organized?
- What Are Neurons and How Do They Transmit Signals?
- What Are the Types of Neurons and Their Functions?
- How Does the Thalamus Function as a Relay Center?
- What Is the Role of the Facial Nerve in Motor and Sensory Function?
- What Is Hemiplegia and What Causes It?
- What Is the Function of Microglia in the Central Nervous System?
- What Is the Brachial Plexus and Why Is It Important?
- What Is the Difference Between White and Gray Matter?
- Why Are Spinal Taps Performed Below the L3 Vertebra?
- What Is Bell's Palsy and What Nerve Is Affected?
- Which Brain Structure Controls Voluntary Actions?
- How Do Schwann Cells Compare to Oligodendrocytes?
- What Is the Sensory Function of the Parietal Lobe?
- What Is the Midbrain's Role in Reflex Control?
- Why Must Cerebrospinal Fluid (CSF) Remain in Motion?
- What Is the Function of the Pia Mater?
- How Is the Peripheral Nervous System Functionally Divided?
- What Does the Transverse Fissure Indicate in Brain Anatomy?
When someone suffers a stroke or experiences sudden paralysis, the answers lie deep within the nervous system. This lesson breaks down how signals travel, how reflexes work, and how different brain parts coordinate to keep us alive. Students will explore structure, function, and disorders with precision and clarity.
What Is the Nervous System and Why Is It Vital to Human Survival?
The nervous system is the master control and communication system of the body. It integrates internal and external stimuli to initiate appropriate responses for survival, coordination, and adaptation. This system ensures that the body can sense, interpret, and respond to its environment rapidly and accurately.
- The nervous system is divided into the central nervous system (CNS) and peripheral nervous system (PNS).
- The CNS includes the brain and spinal cord, acting as the integration and command centers.
- The PNS includes all neural structures outside the CNS, serving as a communication line between the body and the CNS.
Together, these systems regulate everything from muscle contraction and glandular secretion to emotions, reflexes, and consciousness.
(161).jpg)
How Is the Nervous System Structurally and Functionally Organized?
The nervous system's structure is intricately linked to its function. It is divided into various subdivisions to simplify its complexity.
- The central nervous system (CNS) is responsible for processing and interpreting sensory input and issuing instructions.
- The peripheral nervous system (PNS) connects the CNS to the rest of the body and is further divided into:
- Sensory (afferent) division: Carries information from sensory receptors to the CNS.
- Motor (efferent) division: Transmits impulses from the CNS to effector organs.
The motor division includes:
- The somatic nervous system: Controls voluntary movements via skeletal muscles.
- The autonomic nervous system: Controls involuntary functions and is divided into:
- Sympathetic division (fight or flight response).
- Parasympathetic division (rest and digest activities).
What Are Neurons and How Do They Transmit Signals?
Neurons, or nerve cells, are the functional units of the nervous system. Each neuron is specialized to transmit electrical impulses.
- Cell body (soma): Contains the nucleus and organelles.
- Dendrites: Receive electrical messages from other cells.
- Axon: Carries impulses away from the cell body.
- Synapse: A chemical or electrical junction between neurons (not a structural part of the neuron itself).
Neurons use neurotransmitters such as acetylcholine and dopamine to communicate across synapses.
What Are the Types of Neurons and Their Functions?
Neurons are functionally classified based on the direction in which they transmit impulses:
- Sensory (afferent) neurons: Transmit impulses from sensory receptors to the CNS.
- Motor (efferent) neurons: Convey commands from the CNS to muscles or glands.
- Interneurons: Connect neurons within the CNS and process information.
Motor neurons control muscle movement, while sensory neurons provide input about the environment or internal body conditions.
How Does the Thalamus Function as a Relay Center?
The thalamus is located in the diencephalon and serves as the brain's major relay station.
- It receives incoming sensory signals (except smell) and relays them to appropriate areas of the cerebral cortex.
- It filters out unnecessary information and plays a role in consciousness, alertness, and sleep regulation.
Damage to the thalamus can lead to sensory deficits, impaired arousal, or even coma.
What Is the Role of the Facial Nerve in Motor and Sensory Function?
The facial nerve (cranial nerve VII) is responsible for a range of critical functions:
- Innervates facial muscles for expression (e.g., smiling, frowning).
- Carries taste sensations from the anterior two-thirds of the tongue.
- Stimulates lacrimal (tear) and salivary glands.
Injury to this nerve results in facial asymmetry and conditions such as Bell's palsy.
What Is Hemiplegia and What Causes It?
Hemiplegia is a neurological condition characterized by paralysis on one side of the body.
- It results from lesions in the brain's motor cortex or corticospinal tract, commonly caused by stroke (cerebrovascular accident).
- It differs from paraplegia (paralysis of lower limbs) and quadriplegia (paralysis of all limbs).
Effective rehabilitation focuses on physical therapy and re-learning motor skills through neuroplasticity.
What Is the Function of Microglia in the Central Nervous System?
Microglia are small glial cells that serve as the primary immune defense in the CNS.
- They act as macrophages, engulfing pathogens, debris, and dead neurons.
- Microglia constantly survey the CNS for abnormalities.
- They release signaling molecules that mediate inflammation and repair.
Their dysregulation has been linked to neurodegenerative diseases like Alzheimer's.
What Is the Brachial Plexus and Why Is It Important?
The brachial plexus is a complex network of nerves arising from spinal segments C5–C8 and T1.
- It supplies motor and sensory innervation to the upper limbs.
- Major nerves from the brachial plexus include the radial, ulnar, and median nerves.
Injury to this plexus can result in sensory loss, muscle weakness, or paralysis of the arm.
What Is the Difference Between White and Gray Matter?
The nervous system contains two distinct types of tissue:
- White matter: Consists of myelinated axons responsible for signal transmission.
- Gray matter: Composed of neuronal cell bodies and unmyelinated fibers for processing and integration.
White matter forms the bulk of the inner spinal cord and outer brain regions, while gray matter forms the cerebral cortex and spinal cord core.
Why Are Spinal Taps Performed Below the L3 Vertebra?
Spinal taps, or lumbar punctures, are conducted below L3 to avoid spinal cord injury.
- The spinal cord terminates around L1–L2 in adults.
- Below this point, the cauda equina (nerve roots) can be safely pushed aside.
This procedure collects cerebrospinal fluid for diagnosing infections (like meningitis), hemorrhages, and autoimmune diseases.
What Is Bell's Palsy and What Nerve Is Affected?
Bell's palsy is an acute condition involving temporary facial paralysis.
- It is caused by inflammation or viral infection of the facial nerve (VII).
- Symptoms include unilateral drooping, loss of nasolabial fold, and drooling.
Prognosis is typically good, with most cases resolving within weeks to months.
Which Brain Structure Controls Voluntary Actions?
The cerebrum is responsible for initiating voluntary movement.
- It includes the primary motor cortex in the frontal lobe.
- It controls functions such as speech, conscious movement, problem-solving, and planning.
Cerebral dominance (left or right brain) affects language and handedness.
How Do Schwann Cells Compare to Oligodendrocytes?
Both cell types myelinate axons, but in different parts of the nervous system:
- Schwann cells myelinate axons in the PNS.
- Oligodendrocytes perform this role in the CNS.
Each Schwann cell wraps around a single axon segment, while oligodendrocytes extend processes to multiple axons.
What Is the Sensory Function of the Parietal Lobe?
The parietal lobe is primarily responsible for processing sensory input.
- It integrates tactile information like pressure, pain, and temperature.
- It helps in spatial navigation and proprioception.
Lesions in the parietal lobe can lead to neglect syndrome or poor motor coordination.
What Is the Midbrain's Role in Reflex Control?
The midbrain is the uppermost portion of the brainstem and functions as a reflex center.
- It coordinates reflexes related to visual and auditory stimuli.
- It helps control pupil dilation and eye movements.
Midbrain damage can impair consciousness, reflexes, and motor control.
Why Must Cerebrospinal Fluid (CSF) Remain in Motion?
Cerebrospinal fluid cushions the CNS and must circulate freely to function properly.
- CSF removes waste and delivers nutrients.
- Stagnation can increase intracranial pressure and impair neuronal activity.
Hydrocephalus and meningitis are conditions associated with CSF flow disruption.
What Is the Function of the Pia Mater?
The pia mater is the innermost of the three meninges surrounding the brain and spinal cord.
- It adheres tightly to the brain surface and supports blood vessels.
- It participates in forming the blood-brain barrier.
In lab dissection, the pia mater is difficult to separate due to its intimate attachment to neural tissue.
How Is the Peripheral Nervous System Functionally Divided?
The PNS consists of:
- Sensory (afferent) division: Carries signals from receptors to the CNS.
- Motor (efferent) division: Transmits commands from the CNS to muscles and glands.
This ensures the body can detect environmental changes and react accordingly.
What Does the Transverse Fissure Indicate in Brain Anatomy?
The transverse fissure is a deep groove that separates the cerebrum from the cerebellum.
- It marks a key boundary between centers for voluntary control and coordination.
- During dissection, it helps students differentiate between brain regions.
Identifying fissures is critical in anatomical orientation and understanding brain function.
Rate this lesson:
Back to top