Human Physiology: Autonomic Nervous System (ANS)

• Human Physiology BIOL 2052 A taught by Dr. Cristina V Dieni, [email protected], phone: 942-4291, ext. 2248, office: BGSC213.

Autonomic Nervous System (ANS)

• Part of the PNS, operating autonomously and continuously without conscious effort.
• ANS regulates visceral activities by controlling smooth muscles, cardiac muscles, and glands.
• It oversees heart rate, blood pressure, breathing rate, body temperature, and maintains homeostasis.
• Portions of the ANS respond during emotional stress and prepare the body for strenuous activity.
• ANS activities are regulated by reflexes originating from receptors in the viscera and skin.

Autonomic Motor Pathway

• Composed of two autonomic motor neurons and a visceral effector.
• Involves two autonomic motor neurons in series: a preganglionic neuron extending from the CNS to an autonomic ganglion, and a postganglionic neuron extending from the ganglion to the effector (smooth muscle, cardiac muscle, or gland).
• A ganglion is a cluster of neuronal cell bodies in the PNS.
• Dendrites of a preganglionic neuron of the autonomic motor pathway are in the central nervous system.

Organization of the Parasympathetic and Sympathetic Nervous Systems

• The parasympathetic nervous system originates in the brain stem and sacral region of the spinal cord.
• The sympathetic nervous system originates in the thoracic and lumbar regions of the spinal cord.

Neuroeffector Junction

• The synapse between an autonomic postganglionic neuron and a visceral effector.
• Axon terminals of the postganglionic neuron lack synaptic end bulbs, instead exhibiting varicosities, which contain synaptic vesicles with neurotransmitter.
• Receptors for neurotransmitters are located along the entire surface of the effector cell, not confined to a specific region.
• Autonomic postganglionic neurons release neurotransmitters from varicosities at the ends of axon terminals.

Signal Transmission at a Neuroeffector Junction

• Action potential arrives at varicosity.
• Voltage-gated Ca2+ channels open, and Ca2+ enters.
• Ca2+ influx triggers neurotransmitter release.
• Neurotransmitter binds to receptors on the plasma membrane of effector cell.
• G protein activation leads to excitation or inhibition of the effector cell.

Neurotransmitters and Receptors in the ANS

• The ANS uses two types of neurotransmitters and receptors: Cholinergic and Adrenergic.
• Cholinergic involves:
• Neurotransmitter: Acetylcholine released by preganglionic neurons of both systems and by postganglionic neurons of the parasympathetic nervous system.
• Nicotinic receptors are found on postganglionic neuron cell bodies.
• Muscarinic receptors are found on target tissue of the parasympathetic nervous system.
• Adrenergic involves:
• Neurotransmitters: Norepinephrine released by postganglionic cells of the sympathetic nervous system and epinephrine released by chromaffin cells of the adrenal medulla.
• Receptors: alpha and beta.

Summary of the Autonomic Nervous System

• Parasympathetic preganglionic neurons release Acetylcholine (ACh) which binds to nicotinic receptors on postganglionic neurons, which in turn release ACh to bind muscarinic receptors on effector cells.
• Sympathetic preganglionic neurons release ACh which binds to nicotinic receptors on postganglionic neurons, which in turn release Norepinephrine (NE) to bind adrenergic receptors on effector cells.

ANS Functions

• Autonomic tone is regulated by the hypothalamus.
• Body organs receive constant innervation by both branches.
• One branch will turn up while the other turns down for the desired effect.

ANS Functions

• Parasympathetic effects: Rest and digest, conserve body energy, promote breakdown and absorption of food.
• Remember SLUDD: Salivation, Lacrimation, Urination, Digestion, and Defecation.
• Sympathetic effects: Fight or flight, support vigorous physical activity, and rapid ATP production.
• “E” = excite, emergency, exercise, embarrassment.
• Sympathetic effects are more diffuse and affect many organs, more longer lasting.

Autonomic Reflexes

• Autonomic reflexes maintain homeostasis.
• They consist of a sensory receptor, sensory neuron, integrating center, autonomic motor neurons, and a visceral effector.

Autonomic Control Centers

• Located in the brain and spinal cord.
• control centers include: Cardiovascular and Respiratory.

Sensory Systems

• Contribute to homeostasis by detecting, conducting, and processing information about the external or internal environment.
• Consists of sensory receptors, neural pathways, and parts of the CNS that process information.
• Major Sensory Systems:
• Somatic sensory system
• Visual system
• Olfactory (smell) system
• Gustatory (taste) system
• Auditory (hearing) system
• Vestibular (equilibrium) system

Process of Sensation

• Involves four steps: -Stimulation of the sensory receptor -Transduction of the stimulus -Generation of action potentials -Integration of sensory input

Types of Sensory Receptors

• Mechanoreceptors: Sensitive to mechanical stimuli like deformation.
• Thermoreceptors: Detect changes in temperature.
• Photoreceptors: Detect light striking the retina.
• Chemoreceptors: Detect chemicals in the mouth, nose, and body fluids.
• Nociceptors: Respond to painful stimuli from physical or chemical tissue damage.

Sensory Receptors

• Peripheral endings of sensory neurons may be encapsulated nerve endings with dendrites, or free nerve endings.
• Sensory receptor, that is a separate cell.
• Release of neurotransmitter after triggering from stimuli.

Receptive Fields

• Receptive fields exist for somatic sensory neurons, visual neurons in the eye, olfactory receptor cells in the nose, auditory neurons in the inner ear and taste neurons in the tongue.

Receptive Fields Cont.

• Sensory neurons can have different receptive fields. -Separate receptive fields do not have overlapping areas, so each stimulus can be differentiated on different sensory neurons. -Sensory neurons can also have sensory receptive fields that overlap.

Modality and Labelled Lines

• Sensory information is transmitted via labeled lines, specific neural pathways for each sense.

Stimulus Intensity

• Encoded in frequency of action potentials generated.
• Encoded by the number of sensory receptors activated.

Adaptation of Receptors

• Rapidly adapting receptors fire briefly when stimulus is applied and may then stop even though the stimulus continues. -Can be slowly adapting receptors.

Sensory Pathways to the Brain

• Utilize a series of neurons to relay information: first-order, second-order, and third-order.

Tactile Sensations

• Encompass a variety of sensations:Touch, Pressure, Vibration, Itch, and Tickle.

Transduction of Tactile Stimuli

Pacinian corpuscles respond to vibration. Mechanically-gated cation channels open due to membrane deformation. Influx of Na+ and Ca2+ causes a depolarizing receptor potential.

Thermal Sensations

• Detected by thermoreceptors.
• Cold receptors activated by temperatures between 10°C-35°C (50-95°F).
• Warm receptors activated by temperatures between 30-45°C (86-113°F).
• Warm receptors are fewer than cold.

Pain Sensations

• Protect the body from stimuli that can cause tissue damage.
• Types of nociceptors: mechanical, thermal, and polymodal.

Proprioceptive Sensations

• Provide information about muscle and joint position.

The Olfactory Epithelium

• Contains olfactory neurons, supporting cells and olfactory glands.

Olfactory Transduction

• Odorant molecules bind to olfactory receptor proteins.
• G protein activation leads to cAMP production.
• Cation channels open, causing depolarizing receptor potential and action potential generation.

The Olfactory Pathway

• Extends through the Olfactory bulb -> Olfactory tract -> Olfactory cortex.
• Receptor cell sends signal to the Mitral cell in the Glomeruli.

Taste Buds

• Contain the receptors for taste.

Transduction of Taste

• Each taste has its own specialized transduction but they all connect to neurotransmitter release to first order taste neuron.
  • Salty tastants via Na+ channels.
  • Sour tastants via H+ channels.
  • Sweet, bitter, and umami tastants via receptors.

The Gustatory Pathway

• Extends from taste receptors via cranial nerves to the gustatory cortex.

Accessory Structures of Eye

• Accessory structures protect, lubricate, and move the eye.

Functional Components of the Eye

• The anterior cavity contains aqueous humor. It includes the cornea, iris, pupil and lens.
• Zunular fibers connect ciliary body and lens.
• The Posterior cavity contains vitreous humor. Includes the retina, choroid and sclera.
• Optic disc connects to the Optic II nerve.

Organization of the Retina

• Layers include the Pigmented layer, Photoreceptor cell layer (rods and cones), and Neural layer (bipolar cells and ganglion cells).
• Path of light goes to pigmented and photoreceptor layer.
• Direction of processing flows from photoreceptor layer to neural layer.

The Eye Forms Images of Objects on the Retina

• The eye refracts light to focus images on the retina.
• Refraction of light by the cornea and lens to focus image.

Adjustment of the Image on the Retina

• Accommodation is the Increase in curvature of the lens.

Disorders of the Eye

• Normal is termed "emmetropic" eye.
• Nearsighted is termed "myopic" eye. Corrected by using a concave lens.
• Farsighted is termed "hyperopic" eye. Corrected by using a convex lens.

Photoreceptors

• Two types are required for normal vision: Rods and Cones.
• These are sensitive to light Rods = highly sensitive, Cones = low sensitivity to light.

The Visual Pathway

• Extends from photoreceptors to the visual areas of the brain.
• Eyes receive info from the left visual field and the right visual field .

Ear Components

• External ear comprises of Pinna, External auditory canal, Tympanic membrane, Cerumen, Round Window.
• Middle ear comprises of Malleus, Incus and Stapes in oval window.
• Inner ear comprises of Helicotrema, Cochlea, Perilymph, Cochlear branch of vestibulocochlear (VIII) nerve.

Sound Waves

• Sound waves are generated from a vibrating object which affects the pitch and intensity.
• Pitch is determined by frequency
• Intensity has an amplitude, measured in decibels.

Transmission of Sound Waves

• Sound waves -> External auditory canal -> Tympanic membrane -> Malleus, Incus, Stapes in perilymph Helicotrema/Apex.

Sound Transduction

• Transmitted by the hair cells in Inner and Outer parts.
• Inner hair cells are responsible for sound transduction.
• Outer hair cells enhance the sensitivity of inner hair cells.

Sound Discrimination on the Basilar Membrane

• Depends on Basilar membrane for region and loudness.

The Auditory Pathway

• Medial geniculate nucleus of thalamus -Cochlear branch of vestibulocochlear (VIII) nerve
• • Low to High frequency sounds.

Equilibrium

• Equilibrium is the state of balance.
• Utilizes Otolithic organs in the utricle and saccule. Otoliths are utilized to detect linear acceleration or deceleration + detect head tilt.
• Utilizes Semicircular ducts. Detect rotational acceleration deceleration.

Utricle and Saccule

• These contain maculae.
• Contains Vestibular branch of vestibulocochlear (VIII) nerve
• Contains Otoliths that are supported by hair and supportive cels.

Semicircular Ducts

• Contain Ampulla and crista in the center.
• This helps with rotational movement.

Equilibrium Pathway

• Thalamus - Vestibular cortex
• Nuclei cranial nerves that control eye movement.
• Cerebellum + Vestibular nucleui.