W7 | Nervous System

Nervous System

Functions: '

• maintaining homeostasis

• receiving sensory input

• integrating information

• controlling muscles and glands

• mental activity

Central Nervous System (CNS)

• Brain and spinal cord

• Responsible for decision-making and processing information.

Peripheral Nervous System (PhS)

• Detects stimuli and sends information between the CNS and the body.

1. Central Nervous System (CNS)

2. Peripheral Nervous System (PNS)

2 divisions of the nervous system

Sensory Division (Afferent)

• Sends signals from receptors to the CNS.

Motor Division (Efferent)

• Sends signals from the CNS to muscles and glands.

1. Sensory Division (Afferent)

2. Motor Division (Efferent)

2 Peripheral Nervous System Division

Somatic Nervous System

• Voluntary control of skeletal muscles.

  
  

Autonomic Nervous System

• Involuntary control of smooth/cardiac muscle and gland functions.

1. Somatic Nervous System

2. Autonomic Nervous System

2 Motor Divisions of the PNS

Sympathetic Division

• Fight or flight response

Parasympathetic Division

• Rest and digest functions

Enteric Nervous System

• Controls the digestive tract

1. Sympathetic Division

2. Parasympathetic Division

3. Enteric Nervous System

Three Divisions of the Autonomic Nervous System

Neurons

• The functional, electrically excitable cells of the nervous system are crucial for communication and control of body functions.

Glial Cells

• Support neurons, providing structural support, nourishment, and protection.

1. Neuron Cell Body (Soma)

2. Dendrites

3. Axons

Neuron Structures:

Neuron Cell Body (Soma)

• Contains the nucleus and organelles like RER (Nissl bodies) for protein synthesis, essential for neuron function.

  
  

Dendrites

• Short branched extensions that receive signals from other neurons or sensory receptors and generate electrical currents toward the neuron cell body.

  
  

Axon

• A single, long extension transmitting electrical impulses (action potentials) away from the cell body to other neurons or effectors.

Collateral axons

• Branches of axons that can form multiple synapses at their ends.

1. Multipolar Neurons

2. Bipolar Neurons

3. Pseudo-Unipolar Neurons

4. Anaxonic Neurons

Structural Classifications of Neuron Types

Multipolar Neurons

• Have many dendrites and one axon

• Most common neurons found in both the CNS and PNS.

  
  

Bipolar Neurons

• Have one dendrite and one axon

• Specialized for sensory functions and found in organs like the retina and olfactory system.

  
  

Pseudo-Unipolar Neurons

• A single process divides into two branches: one extending toward the sensory receptor and the other toward the CNS.

  
  

Anaxonic Neurons

• Lack a distinct axon, have only dendrites, and communicate via graded potentials rather than action potentials. Found in the brain and retina.

1. Sensory (Afferent) Neurons

2. Motor (Efferent) Neurons

3. Interneurons

Functional Classifications of Neuron Types

Sensory (Afferent) Neurons

• Conduct action potentials from sensory receptors toward the CNS.

Motor (Efferent) Neurons

• Transmit action potentials away from the CNS to muscles or glands to produce responses.

  
  

Interneurons

• Connect sensory and motor neurons within the CNS and play a role in complex processing.

Glial Cells

• Support neurons

• Provide structural support, nourishment, and protection

AEMO

1. Astrocytes

2. Ependymal Cells

3. Microglia

4. Oligodendrocytes

Glial Cells in the CNS

Astrocytes

• Star-shaped cells that form a framework by covering surfaces of neurons, blood vessels, and pia mater

• Help form the blood-brain barrier and regulate neurotransmitter activity.

  
  

Ependymal Cells

• Line the ventricles of the brain and central canal of the spinal cord

• Specialized ependymal cells help form choroid plexuses that secrete CSF.

  
  

Microglia

• CNS-specific immune cells that become phagocytic in response to inflammation and digest necrotic tissue, microorganisms, and foreign substances.

Oligodendrocytes

• Form the myelin sheath in the CNS, insulating axons to improve the speed of nerve impulse transmission.

1. Schwann Cells

2. Satellite Cells

Glial Cells in the PNS

Schwann Cells

• Form myelin sheaths around axons in the PNS

• Each cell insulates a single axon.

  
  

Neurilemma

• Outermost layer of the Schwann cell containing its nucleus and cytoplasm.

  
  

Satellite Cells

• Surround neuron cell bodies in sensory and autonomic ganglia

• Provide support and nutrition and protect neurons from heavy metals.

Myelinated Axons

• Axons wrapped by Schwann cells or oligodendrocytes to form a myelin sheath

• Conduct signals faster than unmyelinated axons.

  
  

Myelin Sheath

• Phospholipid-rich insulating covering around axons that speeds signal transmission.

  
  

Nodes of Ranvier

• Gaps between myelinated segments that are essential for saltatory conduction.

  
  

Unmyelinated Axons

• Axons embedded in Schwann cells or oligodendrocytes but lacking multiple membrane layers;

• Conduct signals more slowly due to less insulation.

  
  

Myelin Sheath Development

• Myelination begins in fetal development, enhancing motor coordination and response speed as it progresses.

Gray Matter

• Composed of neuron cell bodies (soma), dendrites, and unmyelinated axons.

• cortex + nuclei

White Matter

• Made up of myelinated axons, which give it a whitish color.

• nerve tracts

  
  

PFCT

1. Neural Plate

2. Neural Folds

3. Neural Crest

4. Neural Tube

Neural Tube Formation in the Brain Development

Cerebrum

• Largest part of the brain

• Divided into left and right hemispheres by the longitudinal fissure.

  
  

Longitudinal fissure

• Divides the cerebrum into left and right hemispheres.

  
  

1. Gyri

2. Sulci

3. Central Sulcus

4. Precentral Gyrus

5. Postcentral Gyrus

Surface Features of the Cerebrum

Gyri

• Folds that increase cortical surface area.

  
  

Sulci

• Grooves between gyri that divide hemispheres into lobes.

Central Sulcus

• Landmark dividing the frontal and parietal lobes.

  
  

Precentral Gyrus

• Primary motor cortex

• Located anterior to the central sulcus.

  
  

Postcentral Gyrus

• Primary somatosensory cortex

• Located posterior to the central sulcus

1. Frontal lobe

2. Parietal lobe

3. Occipital lobe

4. Temporal lobe

5. Insula (Fifth lobe)

Lobes of the Cerebrum

Frontal lobe

• Voluntary motor function, motivation, aggression, mood, and sense of smell.

  
  

Prefrontal cortex

• Part of the frontal lobe that is involved in personality and decision making.

Parietal lobe

• Major center for sensory information excluding smell, hearing, taste, and vision.

  
  

Occipital lobe

• Integrates visual input.

  
  

Temporal lobe

• Evaluates input for smell and hearing

• Important for memory, abstract thought, and judgment.

  
  

Insula (Fifth lobe)

• Located deep within the lateral fissure

• Involved in taste information processing.

Cerebral Cortex

• Gray matter on the outer surface consisting of various neuron types distributed in layers.

  
  

Cerebral Medulla

• White matter between the cortex and nuclei.

1. Association Fibers

2. Commissural Fibers

3. Projection Fibers

Three Main Types of Fibers in Cerebral Medulla

Association Fibers

• Connect areas within the same hemisphere.

  
  

Commissural Fibers

• Connect corresponding areas of both hemispheres, such as the corpus callosum.

  
  

Projection Fibers

• Connect the cerebrum to other brain regions and spinal cord; form the internal capsule.

Basal Nuclei

• Largest nuclei in the brain

• Located beneath the cortex and involved in motor function control.

  
  

Limbic System

• Group of structures within the cerebrum and diencephalon forming a ring around the diencephalon

• Involved in motivation, emotion, learning, and memory.

Diencephalon

• Located between the brainstem and cerebrum

Thalamus

• Largest part of the diencephalon

• Processes sensory information and sends projections to the cerebral cortex; involved in mood and emotion regulation

Subthalamus

• Small area beneath the thalamus containing subthalamic nuclei involved in motor function control.

  
  

Epithalamus

• Small region above and behind the thalamus

Hypothalamus

• Lowest part of the diencephalon

• Regulates autonomic nervous system functions, thirst, hunger, sex drive, biological clock, emotional responses, and behaviors related to mood and motivation.

  
  

Brainstem

• Connects the spinal cord to the base of the brain

Composed of:

1. Medulla oblongata

2. Pons

3. Midbrain.

Medulla Oblongata

• Most inferior part of the brainstem

• Contains centers for vital reflexes regulating heart rate, blood vessel diameter, respiration, swallowing, vomiting, coughing, and sneezing.

  
  

Pons

• Located just superior to the medulla oblongata

• Contains pontine nuclei and centers involved in sleep and respiration.

  
  

Pontine Nuclei

• Relay information from the cerebrum to the cerebellum.

  
  

Pontine Sleep Center

• Initiates rapid eye movement sleep.

  
  

Pontine Respiratory Center

• Works with medullary centers to control respiration.

  
  

1. Pontine Nuclei

2. Pontine Sleep Center

3. Pontine Respiratory Center

Three kinds of Pons

Midbrain

• Superior division of the brainstem.

  
  

Cerebellum

• Controls muscle movement and tone, governs balance, regulates the extent of intentional movement, and is involved in learning motor skills.

  
  

1. Flocculonodular Lobe

2. Vermis

3. Lateral Hemisphere

Parts of the Cerebellum

Lateral Hemisphere

• Involved in planning, practicing, and learning complex movements.

Vermis

• Central, worm-shaped part involved in posture, locomotion, and fine motor coordination.

  
  

Flocculonodular Lobe

• Small, inferior part of the cerebellum that controls balance and eye movements

Cranial Nerves

• Transmit and relay information to inform the brain

• Connect directly to the brain (unlike spinal nerves)

1. Sensory function

2. Somatic Motor

3. Parasympathetic function

Functions of the Cranial Nerves

1. Includes special senses and general senses such as touch and pain.

2. Controls skeletal muscles; proprioceptive fibers provide awareness of body position.

3. Regulation of glands, smooth muscle, and cardiac muscles

   
   

1. Olfactory Nerve (I)

2. Optic Nerve (II)

3. Oculomotor Nerve (III)

4. Trochlear Nerve (IV)

5. Trigeminal Nerve (V)

6. Abducens Nerve (VI)

7. Facial Nerve (VII)

8. Vestibulocochlear Nerve (VIII)

9. Glossophrayngeal Nerve (IX)

10. Vagus Nerve (X)

11. Accessory Nerve (XI)

12. Hypoglossal Nerve (XII)

12 Cranial Nerves

Olfactory CN I

• Sensory; smell

Optic CN II

• Sensory; vision

Oculomotor CN III

• Eye muscles; pupil size/lens shape

Trochlear CN IV

• somatic motor

• Superior oblique

Trigeminal CN V

• somatic & sensory function

• Mastication + facial sensation

Abducens CN VI

• Lateral rectus

Facial CN VII

• Facial expression + taste + glands

Vestibulocochlear CN VIII

• Hearing + balance