Emotions and Stress Responses

Emotions & Stress Responses

Autonomic and Hormonal Responses

• The sympathetic nervous system activates the fight-or-flight response, increasing heart rate, blood pressure, and respiration.
• The hormonal response pathway (HPA Axis) begins with the hypothalamus releasing Corticotropin-Releasing Factor (CRF).
• The anterior pituitary gland then releases Adrenocorticotropic Hormone (ACTH).
• The adrenal cortex releases cortisol, increasing blood sugar and metabolic rate to prepare the body for action under stress.

Theories of Emotional Experience

• The James-Lange Theory suggests that a stimulus leads to autonomic arousal and muscle tension, which then results in an emotion label.
• This theory emphasizes that perception of body changes leads to emotional labeling.
• Evidence supporting this theory includes reports of less intense emotions from people with spinal cord injuries.
• Those with Locked-in Syndrome also have reduced emotional experience due to the lack of body feedback.
• The Cannon-Bard Theory posits that a stimulus triggers brain processing, leading to simultaneous arousal and emotion.
• Emotions and physical responses occur independently but simultaneously.

The Amygdala

• The amygdala's structure includes multiple nuclei, with the central nucleus being key for emotional processing.
• The amygdala receives sensory input from the thalamus and cortex.
• Stimulation results in fear, agitation, or aggression.
• Damage leads to decreased emotional response, stress hormones, conditioned emotional response (CER), and memory.
• It is the target site for benzodiazepines like Valium, which reduces anxiety.

Facial Emotional Expression & Recognition

• Paul Ekman identified universal facial expressions for happiness, sadness, anger, and disgust
• These expressions are innate, shown even in blind individuals.
• The left side of the face expresses more emotion and is controlled by the right hemisphere.
• Facial recognition relies on the amygdala and right cortex to recognize others' emotions.

Prefrontal Cortex & Emotion Regulation

• Damage to the orbitofrontal cortex can cause indifference, social inappropriateness, and lack of inhibition.
• It can also lead to decreased emotional expression, planning, and judgment.
• A prefrontal lobotomy/leucotomy, performed on psychiatric patients, targets the orbital frontal cortex, resulting in emotional dulling.

Neurotransmitters & Hormones

• Low serotonin levels are linked to increased aggression.
• High testosterone levels are linked to increased aggression

Sensation and Perception

Definitions

• Stimulus refers to environmental energy/input.
• Sensation is the conversion of external energy into neural signals by sensory neurons.
• Transduction is the actual process of converting a stimulus into electrical signals.
• Perception involves the interpretation and mental organization of sensory input, which is psychological and subjective.

Hearing / Auditory System

Sound Characteristics

• Frequency (Hz) relates to pitch, with the human range being 20-20,000 Hz.
• Amplitude relates to loudness.
• Complexity determines timbre, or tone quality.

Ear Structure

• The outer ear includes the pinna, which collects sound.
• The middle ear consists of the eardrum (tympanic membrane) and ossicles.
• The ossicles are small bones including the hammer (malleus), anvil (incus), and stirrup (stapes).
• The inner ear contains the cochlea, a fluid-filled, snail-shaped structure.
• The oval window is where the stapes transmits vibrations.
• The basilar membrane holds hair cells (sensory neurons).
• Hair cells detect movement in fluid, which triggers neurotransmitter release, leading to action potentials in the auditory nerve (CN VIII).

Pitch Perception Theories

• Place Theory suggests high-pitched sounds stimulate the base of the basilar membrane (short distance).
• Low-pitched sounds travel to the apex (longer distance).
• Frequency Theory suggests pitch perception is based on the frequency of action potentials.

Auditory Pathway

• Sound travels through the cochlea and the auditory nerve (CN VIII).
• The signal then progresses to the dorsal cochlear nucleus, crosses the midline, and goes to the inferior colliculus and the medial geniculate nucleus (MGN) of the thalamus.
• Finally, it reaches the primary auditory cortex in the temporal lobe.

Vision / Visual Perception

Light Properties

• Wavelength corresponds to hue (color).
• Amplitude determines brightness.
• Purity corresponds to saturation.
• These properties are perceived, not physical.

Structure of the Eye

• The cornea is a clear, outer covering that helps focus incoming light.
• The iris is the colored part of the eye and controls the size of the pupil.
• The pupil is the hole in the center of the iris, where light enters.
• The lens focuses light onto the retina, inverting and reversing the image.
• The retina contains sensory cells (photoreceptors) that convert light into electrical signals sent to the brain.
• Photoreceptors include rods (for black and white vision, more sensitive to light) and cones (for color vision, function best in bright light).
• The fovea is the area of the retina with the sharpest vision and contains only cones, located directly behind the pupil.
• The optic disk (blind spot) is where the optic nerve exits the eye and contains no rods or cones, making it insensitive to light.

Anatomy of the Retina

• Photoreceptors consist of rods and three types of cones (red, green, blue).
• Rhodopsin is a visual pigment found in rods.
• In light, rhodopsin breaks down into retinal and opsin.
• Adapting from light to dark involves rhodopsin regenerating slowly.
• Adapting from dark to light involves rhodopsin breaking down quickly.
• Bipolar cells relay signals from photoreceptors to ganglion cells.
• Ganglion cells send visual information to the brain through the optic nerve.
• Horizontal and amacrine cells allow side-to-side communication between cells in the retina, helping process visual information.

Light-Dark Vision

• Retinal ganglion cells continuously fire action potentials, even in the dark.
• "On" cells are excited by light in the center of their receptive field and inhibited by light on the edges.
• "Off" cells are inhibited by light in the center and excited by light on the edges.

Color Vision

• Cones are responsible for detecting different wavelengths of light (color).
• There are three types of cones: red, green, and blue.

Theories of Color Vision

• Trichromatic Theory proposes that all visible colors are made from red, green, and blue light
• This theory is based on the presence of three types of cones in the eye.
• It explains color blindness as a result of missing or malfunctioning red, green, or blue cones.
• Opponent Process Theory suggests we have opposing color pairs: red vs. green and blue vs. yellow.
• Activation of one color inhibits the perception of the other and explains negative afterimages.
• The Opponent Process Theory also supports the idea of yellow as a primary color.

Color Vision Theories

• Trichromatic Theory explains how rods and cones (photoreceptors) function.
• Opponent Process Theory explains how retinal ganglion cells and the brain process color information.
• Both theories are partially correct.

Visual Pathways

• Information from both eyes splits into left and right visual fields.
• Signals are sent to the thalamus and then to the primary visual cortex in the occipital lobe.

Visual Processing in the Cortex

• The primary visual cortex (striate cortex) is located in the occipital lobe.
• The fovea gets more cortical space due to high visual acuity because of topographic organization.

Two Visual Streams

• The dorsal stream ("Where/How" pathway) goes from the striate cortex to the posterior parietal lobe and is involved in perception of location and movement.
• The ventral stream ("What" pathway) goes from the striate cortex to the inferior temporal lobe and is involved in object perception and recognition.

The Body Senses (Somatosensation)

Skin Senses: Touch and Pressure

• Non-painful stimuli travel via sensory receptors in the skin and muscles along a distinct neural pathway.
• This pathway includes afferent nerves, the dorsal horn of the spinal cord, crossing the midline in the medulla, traveling to the ventral posterior thalamus, and ending in the primary somatosensory cortex (parietal lobe).
• This pathway is known as the Dorsal Column Pathway.

Skin Senses: Pain and Temperature

• Pain and temperature are detected by free nerve endings.
• These travel via the Spinothalamic Tract of afferent nerves and the dorsal horn of the spinal cord.
• The signal crosses the midline (lower in the spinal cord), travels to the ventral posterior thalamus, and ends in the primary somatosensory cortex (parietal lobe).

Gate Control Theory

• The brain can inhibit pain signals before they reach conscious perception.
• Psychological and physical factors can influence pain experience.

Vestibular Sense (Balance and Spatial Orientation)

• The inner ear detects balance and spatial orientation
• This information travels via the same cranial nerve as hearing: CN VIII.
• Semicircular canals detect rotational movement.
• Otolith organs (utricle & saccule) detect linear acceleration and head position.
• Otoconia (calcium carbonate crystals) in fluid bend hair cell cilia of the vestibular nerve (CN VIII).
• Signals are sent to the brainstem and cerebellum for balance and coordination.

Motor Systems and Disorders

Pyramidal System (Voluntary Motor Control)

• The primary motor cortex (precentral gyrus of frontal lobe) sends neurons down through the cerebral hemispheres, brainstem (crossing the midline at the medulla), and spinal cord.
• Ventral horn motor neurons in the spinal cord have axons that exit as efferent nerves and synapse on muscle fibers.
• Acetylcholine (ACh) is the neurotransmitter that stimulates muscle contraction.

Motor Coordination Centers

• The cerebellum receives input from the brainstem and spinal cord.
• Functions of the cerebellum include balance, posture, coordination, and the timing of movements.
• The basal ganglia (caudate nucleus, putamen, globus pallidus) receives somatosensory input and sends output to the primary motor cortex.
• It makes movements smoother and more coordinated.

Motor Disorders

Myasthenia Gravis

• Is an autoimmune disorder where the immune system attacks ACh receptors on muscle fibers
• Results in muscle weakness and loss of movement
• Treatments include ACh inhibitors that prolong ACh's effect by blocking the enzyme that breaks it down and Thymectomy, which is the removal of the thymus gland (part of the immune system)

Multiple Sclerosis (MS)

• Is an autoimmune disorder in which the immune system attacks myelin on axons, affecting the central nervous system
• The affected areas vary but involve peripheral nerves.
• Symptoms include motor weakness, numbness, tingling, and other sensory disturbances. Treatments include steroid anti-inflammatory drugs and beta-interferon to alter immune system activity.

Parkinson's Disease

• Is caused by the progressive death of dopamine neurons in the substantia nigra, disrupting basal ganglia function.
• Symptoms include tremors, muscle rigidity, bradykinesia (slowness of movement), and postural and gait disturbances, may progress to dementia.
• Treatments include L-Dopa (dopamine precursor) given with carbidopa to prevent breakdown outside the brain, deprenyl (MAO inhibitor) to prevent dopamine breakdown, direct dopamine agonists, and surgical options like pallidotomy or thalamotomy
• Experimental treatments also include dopamine cell transplants.

Huntington’s Disease

• Is an inherited neurodegenerative disorder involving progressive degeneration of the basal ganglia (especially the caudate-putamen)
• It affects GABAergic and ACh neurons.
• Symptoms begin with motor dysfunctions and memory issues, progressing to dementia, and involuntary jerky movements worsen over time.
• The cause is a defective gene on chromosome 4 that codes for abnormal huntingtin protein, in which longer huntingtin protein correlates with earlier onset.
• The mechanism of neuronal death is unclear.
• There is currently no effective treatment available.