Biology Nervous Systems and Plant Responses

Midterm Coverage

• Sensory Receptors and Mechanisms in Plants
• Sensory Receptors and Mechanisms in Animals
• Sensory and Motor Mechanisms in Humans
• Homeostasis (Nervous and Endocrine)
• Negative Feedback Mechanisms
• Positive Feedback Mechanisms

Sensory and Motor Mechanisms in Humans

• Humans use all five senses to collect information from the environment

Five Senses

• Sight

  • The eyes are the photoreceptors in humans
  • The major parts of the eye include the cornea, lens, retina, iris, and pupil
  • Iris and pupil control the amount of light that enters the eye.
  • The retina contains photoreceptors (rods and cones).
  • The optic nerve connects the eyes to the brain.

• Smell

  • The olfactory epithelium (in the nose) contains chemoreceptors that detect substances in the air.
  • Olfactory epithelium contains chemoreceptors that detect substances in the air.

• Hearing

  • The ears detect vibrations in the environment, perceived as sound.
  • Outer ear catches vibrations
  • Middle ear transmits these vibrations to the inner ear
  • Inner ear contains the cochlea, the spiral organ of Corti detecting sound.

• Touch

  • Mechanoreceptors in the skin detect touch in various forms.
  • Different receptors (e.g., free nerve endings, Ruffini's ending, Merkel's disc, Meissner's corpuscle, Pacinian corpuscle) respond to different types of touch pressure

• Taste

  • Chemoreceptors in the tongue detect substances in food.
  • Gustatory cells (in taste buds) detect chemicals in the tongue and release neurotransmitters.

Homeostasis

• Homeostasis is the maintenance of a relatively constant internal environment.
• Cells are surrounded by fluids (intracellular fluid and interstitial fluid) that need to be maintained to sustain the cell's function.
• Variables such as temperature, volume, and chemical substances can change due to external factors and the body responds in order to maintain normal conditions.

Homeostasis components

• Sensor/receptor: Monitors the value of a variable, detects changes in the internal or external environment which are called stimulus (stimuli).

  • Examples: Baroreceptors (blood pressure), peripheral chemoreceptors (blood pH).

• Control center: Establishes the set point around which the variable is maintained, receives information from the sensors and initiates the response to maintain homeostasis.

  • Example: Hypothalamus (blood pressure, body temperature)

• Effector: Can change the value of the variable, any organ or tissue that collects information from the integrating center and acts to create changes needed to maintain homeostasis.

  • Example: Heart (blood pressure), kidney (blood pressure/water levels)

Divisions of the Nervous System

• Somatic nervous system: controls voluntary activities (e.g., skeletal muscles)

• Autonomic nervous system: controls involuntary activities (e.g., internal organs)

• Sympathetic nervous system: triggers the fight-or-flight response

• Parasympathetic nervous system: regulates the rest-and-digest response

Homeostatic System Pathway

• Communication: Uses nervous and endocrine systems

Afferent Pathway

• Communication flows from receptor to control center

Efferent Pathway

• Communication flows from control center to effector

Feedback Loops

• Negative feedback: Helps maintain homeostasis.
• Positive feedback: Amplifies change from a normal range.

Negative Feedback Mechanisms

• Examples:
  • Temperature regulation
  • Osmoregulation

Positive Feedback Mechanisms

• Examples:
  • Childbirth
  • Lactation

Plant Responses

• Plants respond to external factors like light, water, and gravity.

Plant Hormones

• Auxins: Growth, cell expansion, inducing cell division
• Cytokinins: Cell division, differentiation
• Gibberellins: Growth, flower development
• Ethylene: Fruit ripening, plant aging