Neural Control and Coordination

Neural vs. Endocrine System

Introduction

• Coordination: Organs working together to maintain balance (homeostasis).
• Example: During exercise, muscles need more energy and oxygen, leading to increased breathing, heartbeat, and blood flow.

Neural and Endocrine Systems

• Neural System: Fast coordination through network connections.
• Endocrine System: Slow, chemical coordination using hormones.
• Both systems help organs work together smoothly.

Neural System

Basics

• Neurons: Special cells that detect, receive, and transmit signals.
• Simple Systems: Lower animals like Hydra have simple neuron networks.
• Advanced Systems: Insects have brains and ganglia; vertebrates have even more developed systems.

Human Neural System

Two Main Parts

1. Central Neural System (CNS)
   • Components: Brain and spinal cord.
   • Function: Information processing and control.
2. Peripheral Neural System (PNS)
   • Components: All nerves connected to CNS.
   • Nerve Types:
     • Afferent Fibres: Carry signals from organs to CNS.
     • Efferent Fibres: Carry signals from CNS to organs.

PNS Divisions

• Somatic Neural System
  • Function: Sends signals from CNS to skeletal muscles (voluntary control).
• Autonomic Neural System
  • Function: Sends signals from CNS to involuntary organs and smooth muscles.
  • Subdivisions:
    • Sympathetic Neural System
    • Parasympathetic Neural System

Neuron: The Basic Unit of the Neural System

Parts of a Neuron

• Cell Body: Contains cytoplasm, cell organelles, and Nissl’s granules.
• Dendrites: Short, branching fibers with Nissl’s granules that carry impulses to the cell body.
• Axon: Long fiber ending in synaptic knobs containing neurotransmitters, which carry impulses away from the cell body.

Types of Neurons

• Multipolar Neurons: One axon, two or more dendrites (e.g., in the cerebral cortex).
• Bipolar Neurons: One axon, one dendrite (e.g., in the retina of the eye).
• Unipolar Neurons: One axon only (e.g., in the embryonic stage).

Types of Axons

• Myelinated Axons: Covered by Schwann cells forming a myelin sheath with gaps called nodes of Ranvier (found in spinal and cranial nerves).
• Non-Myelinated Axons: Enclosed by Schwann cells without a myelin sheath (found in the autonomic and somatic neural systems).

Generation and Conduction of Nerve Impulse

Polarized State of Neurons

• Resting State: Neuron membrane is polarized.
• Ion Channels: Selectively allow different ions to pass.
  • More Permeable to K+: Potassium ions.
  • Nearly Impermeable to Na+: Sodium ions.
  • Negatively Charged Proteins: Stuck inside the axon.

Resting Potential

• Inside Axon: High K+, low Na+, negative proteins.
• Outside Axon: Low K+, high Na+.
• Sodium-Potassium Pump: Moves 3 Na+ out and 2 K+ in.
• Result: Outside is positive, inside is negative.

Action Potential (Nerve Impulse)

• Stimulus Applied: Changes membrane permeability at a point (Point A).
• Na+ Influx: Na+ rushes in, inside becomes positive, outside negative.
• Depolarization: Membrane polarity reverses at Point A.

Impulse Conduction

• Current Flow: From Point A (depolarized) to next point (Point B).
• Polarity Reversal: Action potential moves from Point A to Point B.
• Sequence: Repeats along the axon, conducting the impulse.

Restoring Resting Potential

• K+ Outflux: K+ moves out, restoring negative inside, positive outside.
• Ready for Next Impulse: Membrane returns to resting state, ready for new stimulus.

This process ensures that nerve signals can travel quickly and efficiently along neurons.

Transmission of Nerve Impulses

Synapses: Junctions Between Neurons

• Synapse: Where one neuron connects to another.
• Types: Electrical synapses and chemical synapses.

1. Electrical Synapses

• Close Proximity: Neurons are very close.
• Direct Flow: Electrical current flows directly between neurons.
• Fast Transmission: Quicker than chemical synapses.
• Rarity: Rare in the human body.

2. Chemical Synapses

• Separated by Synaptic Cleft: Fluid-filled gap between neurons.
• Neurotransmitters: Chemicals that help transmit the impulse.

How Chemical Synapses Work

1. Impulse Arrival: Action potential reaches the axon terminal.
2. Neurotransmitter Release: Synaptic vesicles move to the membrane, releasing neurotransmitters into the synaptic cleft.
3. Binding to Receptors: Neurotransmitters bind to specific receptors on the post-synaptic neuron.
4. Ion Channels Open: Binding opens ion channels, allowing ions to enter.
5. New Potential: This generates a new action potential in the post-synaptic neuron, which can be excitatory or inhibitory.

This process ensures that nerve impulses can be passed from one neuron to the next, allowing for complex communication within the nervous system.

Central Neural System

The Brain: Command and Control Center

• Functions: Controls movements, body balance, organ functions, temperature, hunger, thirst, sleep cycles, endocrine glands, and behavior.
• Processes: Vision, hearing, speech, memory, intelligence, emotions, and thoughts.

Brain Protection

• Skull: Protects the brain.
• Cranial Meninges: Three layers covering the brain:
  • Dura Mater: Outer layer.
  • Arachnoid: Middle layer.
  • Pia Mater: Inner layer, touching the brain.

Major Parts of the Brain

a. Forebrain

• Components: Cerebrum, thalamus, hypothalamus.
• Cerebrum:
  • Divided: Left and right hemispheres connected by corpus callosum.
  • Cerebral Cortex: Outer layer with folds, called grey matter.
  • Functions: Motor areas, sensory areas, association areas (memory, communication).
• Thalamus: Coordinates sensory and motor signals.
• Hypothalamus:
  • Controls: Temperature, hunger, thirst.
  • Neurosecretory Cells: Release hypothalamic hormones.
• Limbic System: Involves amygdala and hippocampus, regulating emotions, sexual behavior, and motivation.

b. Midbrain

• Location: Between forebrain (thalamus/hypothalamus) and hindbrain (pons).
• Cerebral Aqueduct: Canal passing through.
• Corpora Quadrigemina: Four round swellings (lobes).
• Brain Stem: Formed by midbrain and hindbrain

c. Hindbrain

• Components: Pons, cerebellum, medulla (medulla oblongata).
• Pons:
  • Function: Contains fiber tracts connecting different brain regions.
• Cerebellum:
  • Surface: Highly convoluted for extra neuron space.
  • Function: Coordination of movement and balance.
• Medulla:
  • Connection: Links brain to spinal cord.
  • Control Centers: Regulates respiration, heart reflexes, and gastric secretions.

The hindbrain plays a crucial role in connecting the brain with the spinal cord and regulating essential bodily functions.

Reflex Action and Reflex Arc

Reflex Action:

• Reflex actions are quick, automatic responses to certain stimuli.
• They happen without you thinking about them.
• Example: Touching something hot and pulling your hand away immediately.

Reflex Arc:

• Pathway for reflex actions.
• Involves two main neurons:
  • Afferent Neuron (Receptor):
    • Receives signals from sensory organs.
    • Sends these signals to the central nervous system (CNS) through the dorsal nerve root.
  • Efferent Neuron (Effector):
    • Carries signals from the CNS to muscles or glands to cause a response.

Example: Knee Jerk Reflex

• When a specific spot below your knee is tapped, your leg kicks out.
• This is a simple reflex arc involving sensory and motor neurons.

Sensory Reception and Processing

Sensing Changes:

• Sensory organs (like eyes and ears) detect changes in the environment.
• They send signals to the CNS for processing and analyzing.

How it Works:

• Sensory organs detect changes (like temperature, light, sound).
• They send signals to the brain.
• The brain processes these signals and helps us respond appropriately.

Sensory Organs:

• Eyes: For vision, helping you see objects and their colors.
• Ears: For hearing, allowing you to detect and interpret sounds.

The Eye

Location and Structure:

• Eyes are located in skull sockets called orbits.
• Each eyeball is nearly spherical.

Layers of the Eyeball:

1. External Layer (Sclera and Cornea):
   • Sclera: Dense connective tissue.
   • Cornea: Transparent front part of the sclera.
2. Middle Layer (Choroid, Ciliary Body, and Iris):
   • Choroid: Contains blood vessels, bluish color, thin at the back, thick at the front.
   • Ciliary Body: Thickened front part of the choroid.
   • Iris: Pigmented part, visible as the colored portion of the eye. It surrounds the pupil.
3. Inner Layer (Retina):
   • Retina: Has three layers of cells – ganglion, bipolar, and photoreceptor cells.
   • Photoreceptor Cells:
     • Rods: For low light (twilight) vision, contain rhodopsin.
     • Cones: For daylight and color vision, respond to red, green, and blue light.
   • Blind Spot: Where optic nerves leave the eye, no photoreceptor cells.
   • Macula Lutea: Yellowish spot with the central pit (fovea) for sharp vision.

Parts and Functions:

• Lens: Transparent, held by ligaments, helps in focusing.
• Pupil: Hole in the iris, controls light entry by changing size.
• Aqueous Chamber: Between cornea and lens, contains aqueous humor.
• Vitreous Chamber: Between lens and retina, filled with vitreous humor.

Important Terms:

• Rhodopsin: Light-sensitive protein in rods, derived from Vitamin A.
• Photopigments: Proteins in rods and cones, responsible for detecting light.
• Fovea: Area with dense cones, highest visual acuity.

Mechanism of Vision:

• How Vision Works:
  • Light enters the eye through the cornea and lens.
  • Light is focused on the retina, where it hits rods and cones.

Photopigments and Signal Creation:

• Photopigments:
  • Made of opsin (a protein) and retinal (from Vitamin A).
  • Light causes retinal to separate from opsin.
  • This separation changes the opsin’s structure and alters membrane permeability.
• Generating Signals:
  • Changes in membrane permeability create potential differences in photoreceptor cells.
  • These potential differences generate signals.
  • Signals pass through bipolar cells to ganglion cells, creating action potentials.

Transmission to the Brain:

• Action potentials travel via the optic nerves.
• They reach the visual cortex in the brain.
• The brain analyzes these signals, using memory and experience to recognize the image formed on the retina.

The Ear

Functions:

• Hearing
• Balance

Parts of the Ear:

1. Outer Ear:
   • Pinna: Collects sound vibrations.
   • External Auditory Meatus (Canal): Leads to the ear drum, has fine hairs and wax-secreting glands.
   • Tympanic Membrane (Ear Drum): Vibrates with sound waves.
2. Middle Ear:
   • Ossicles (Three tiny bones):
     • Malleus: Attached to the ear drum.
     • Incus: Middle bone.
     • Stapes: Attached to the oval window of the cochlea.
   • Eustachian Tube: Connects middle ear to pharynx, equalizes pressure on both sides of the ear drum.
3. Inner Ear (Labyrinth):
   • Bony Labyrinth: Series of channels filled with perilymph.
   • Membranous Labyrinth: Inside bony labyrinth, filled with endolymph.
   • Cochlea: Coiled structure for hearing.
     • Scala Vestibuli: Upper part ending at the oval window.
     • Scala Tympani: Lower part ending at the round window.
     • Scala Media: Middle part filled with endolymph.
     • Organ of Corti: Located on the basilar membrane, contains hair cells (auditory receptors) with stereo cilia and covered by the tectorial membrane.

Balance:

• Vestibular Apparatus:
  • Semi-Circular Canals: Three canals at right angles, each with an ampulla (swollen base) containing crista ampullaris (balance receptors).
  • Otolith Organs (Saccule and Utricle):
    • Contain macula (balance receptors).

The ear not only helps us hear but also keeps us balanced and upright!

Mechanism of Hearing:

• Sound Wave Journey:
  • Sound waves enter through the external ear and hit the ear drum.
  • The ear drum vibrates in response to these sound waves.
• Transmission of Vibrations:
  • Vibrations travel through the three ear ossicles: malleus, incus, and stapes.
  • The stapes passes these vibrations to the oval window.
• Fluid Waves in the Cochlea:
  • Vibrations from the oval window create waves in the fluids (lymphs) inside the cochlea.
  • These waves cause ripples in the basilar membrane within the cochlea.
• Hair Cell Activation:
  • Movement of the basilar membrane bends the hair cells.
  • Hair cells press against the tectorial membrane, generating nerve impulses.
• Transmission to the Brain:
  • Nerve impulses travel via auditory nerves to the auditory cortex in the brain.
  • The brain analyzes these impulses, allowing us to recognize the sound.

This process helps us convert sound waves into meaningful sounds we can understand!

Chapter Summary:

• The neural system coordinates and integrates functions of all organs.
• It also manages metabolic and homeostatic activities.
• Neurons are the functional units of the neural system.
• Neurons are excitable cells due to ion concentration differences across the membrane.
• The electrical potential difference across the resting neural membrane is called the ‘resting potential’.
• Nerve impulses travel along the axon membrane as a wave of depolarization and repolarization.
• A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron.
• The synaptic cleft may or may not separate these neurons.
• Neurotransmitters are chemicals that transmit impulses at chemical synapses.
• The human neural system has two parts:
  1. Central Neural System (CNS)
  2. Peripheral Neural System
• The CNS consists of the brain and spinal cord.
• The brain has three major parts:
  1. Forebrain
  2. Midbrain
  3. Hindbrain
• The forebrain includes the cerebrum, thalamus, and hypothalamus.
• The cerebrum is divided into two halves connected by the corpus callosum.
• The hypothalamus controls body temperature, eating, and drinking.
• The limbic system is part of the forebrain and manages smell, autonomic responses, sexual behavior, emotional reactions, and motivation.
• The midbrain integrates visual, tactile, and auditory inputs.
• The hindbrain includes the pons, cerebellum, and medulla.
• The cerebellum processes information from the ear’s semicircular canals and the auditory system.
• The medulla controls respiration, cardiovascular reflexes, and gastric secretions.
• The pons connects different brain regions with fiber tracts.
• Reflex action is the involuntary response to peripheral nervous stimulation.
• Sensory organs provide information about environmental changes to the CNS for processing and response.
• The eye’s wall has three layers:
  1. External layer: cornea and sclera
  2. Middle layer: choroid
  3. Innermost layer: retina
• The retina contains rods and cones.
• Cones handle daylight (photopic) and color vision.
• Rods handle twilight (scotopic) vision.
• Light enters through the cornea and lens, forming images on the retina.
• The ear has three parts:
  1. Outer ear
  2. Middle ear
  3. Inner ear
• The middle ear has three ossicles: malleus, incus, and stapes.
• The fluid-filled inner ear is called the labyrinth, with a coiled part called the cochlea.
• The organ of Corti, located on the basilar membrane, contains hair cells that act as auditory receptors.
• Vibrations from the ear drum pass through the ossicles and oval window to the inner ear fluid.
• Nerve impulses are generated and sent to the auditory cortex in the brain.
• The vestibular apparatus in the inner ear helps maintain balance and posture, responding to gravity and movements.